https://www.cbyexample.com/
 
C and C++ are general-purpose computer programming languages. 
They are closely related but with significant differences. 
This guide intends to showcase some of the features and differences of both languages in a user-friendly, progressive format. 
This is not a substitution for in-depth study, but should serve well as an introduction or a refresher.

Inspired by 
Go By Example
https://gobyexample.com/

Javascript By Example
https://javascriptbyexample.com/hello-world




Check out the list of examples below to get started:

Hello World
Types
Initialization
Comments
Switch
Array
Strings
Functions
For Loops
While Loops
Goto
Integer Promotion
Program Arguments
Storage Class Specifiers
Type Qualifiers
Inline Functions
Conditional If
Ternary Operator
Address Resolution Operator
Dereference Operator
Pointers
Pointer Arithmetic
Structs
Union
Input & Output
Bitwise Operations
Typedef
Enumerations
Variadic Functions
Threads
Mutex
Heap Allocation
Assertions
Compound Assignment
Project Structure
Includes
Compilation


C++ only:

Modules
Pass by Reference
Range
Namespaces
Classes
Class Methods
Constructors & Destructors
Encapsulation
Inheritance
Polymorphism
Friend Functions
Templates
Structured Bindings
Lambda Expressions
Exception Handling





C17
#include <stdio.h>

int main() {
	printf("Hello World!\n");
	return 0;
}
C++20
#include <iostream>

int main() {
	std::cout << "Hello World!" << std::endl;
	return 0;
}
output: Hello World!
Types
Every variable has an associated data type that defines its data storage format. Each type requires a certain amount of memory and permits a relevant set of operations.

C17
#include <stdbool.h>  //for bool

int main() {
	int a; // Integer
	unsigned int b; // Unsigned integers only store positive numbers. As a result, they have a higher positive range.
	char c; // Character
	short d; // Short integer
	long e; // Long integer
	float f; // Floating point integer
	double g; // Double-precision floating point integer
	bool h; // Boolean TRUE or FALSE
	return 0;
}
C++20
int main() {
	int a; // Integer
	unsigned int b; // Unsigned integers only store positive numbers. As a result, they have a higher positive range.
	char c; // Character
	short d; // Short integer
	long e; // Long integer
	float f; // Floating point integer
	double g; // Double-precision floating point integer
	bool h; // Boolean TRUE or FALSE
	auto k = 1; // Automatically infer type. Not a type in itself.
	return 0;
}
Initialization
C17
int main() {
	int a = 0;
	char greeting_a[6] = {'H','e','l','l','o','\0'};
	char greeting_b[] = "Hello";
	char* greeting_c = "Hello";
	return 0;
}
C++20
#include <string>

int main() {
	int a = 0; // C-like initialization
	int b {0}; // Uniform initialization. Does not allow narrowing conversions.
	int c(0); // Constructor initialization
	char greeting_a[6] = {'H','e','l','l','o','\0'};
	char greeting_b[] = "Hello";
	std::string greeting_c = "Hello";
	return 0;
}
Comments
Comments are used to write notes and documentation that is to be ignored by the compiler at build time.

C17, C++20
/*
 * Multi-line comments are written like this.
 */

// Single-line comments are written like this.
Switch
Jump to a matching value. Usually cleaner to write than an if/else tree, and faster under the hood.

C17
#include <stdio.h>

int main() {
	int x = 2;
	switch(x) {
	case 1:
		printf("One");
		break; // You must break the search or it will fall through to the next match.
	case 2:
		printf("Two");
		break;
	default: // If no match is found.
		break;
	}
	return 0;
}
C++20
#include <iostream>

int main() {
	int x = 2;
	switch(x) {
	case 1:
		std::cout << "One" << std::endl;
		break; // You must break the search or it will fall through to the next match.
	case 2:
		std::cout << "Two" << std::endl;
		break;
	default: // If no match is found.
		break;
	}
	return 0;
}
output: Two
Array
An array is a collection of items stored at contiguous memory locations. Elements in an array can be accessed randomly using indices.

C17
#include <stdio.h>

int main() {
	int my_array[5];
	int my_array_b[] = {0,1,2,3,4}; // You can init the array from it's elements. Size can be detected automatically here.

    size_t len = sizeof(my_array) / sizeof(my_array[0]);
	for(size_t i = 0; i < len; i++) {
		my_array[i] = i;
	}

	printf("%d\n", my_array[2]);
	return 0;
}
C++20
#include <iostream>
#include <array>

int main() {
	std::array<int, 5> my_array;

	for(size_t i = 0; i < my_array.size(); i++) {
		my_array[i] = i;
	}

	std::cout << my_array[2] << std::endl;
	return 0;
}
output: 2
Strings
A string is an array of characters. C++ supports string types natively, but in C, a string is an array of char data, terminated with the ‘\0’ character.

C17
#include <stdio.h>

int main() {
	char* greeting_c = "Hello";
	return 0;
}
C++20
#include <string>

int main() {
	std::string str1 = "Hello";
	return 0;
}
Functions
Functions are re-usable code segments, created to perform specific tasks.

C17
#include <stdio.h>

// Double the number passed in as 'x', returning the new value to the function caller.
int double_number_a(int x) {
	return 2 * x;
}

// Double the number pointed to by 'x', storing the result in the original variable.
void double_number_b(int* x) {
	*x *= 2;
}

int main() {
	int num = 5;
	printf("%d\n", double_number_a(num));
	printf("%d\n", num);
	double_number_b(&num);
	printf("%d\n", num);
	return 0;
}
C++20
#include <iostream>

// Double the number passed in as 'x', returning the new value to the function caller.
int double_number_a(int x) {
	return 2 * x;
}

// Double the number pointed to by 'x', storing the result in the original variable.
void double_number_b(int* x) {
	*x *= 2;
}

int main() {
	auto num = 5;
	std::cout << double_number_a(num) << std::endl;
	std::cout << num << std::endl;
	double_number_b(&num);
	std::cout << num << std::endl;
	return 0;
}
output: 10
        5
        10
For Loops
Loops allow for continuous execution of a statement or group of statements, usually until a condition is met.

C17
#include <stdio.h>

int main() {
	for(int i = 1; i <= 3; i++) {
		printf("%d\n", i);
	}
	return 0;
}
C++20
#include <iostream>

int main() {
	for (auto i = 1; i <= 3; i++) {
		std::cout << i << std::endl;
	}
	return 0;
}
output: 1
        2
        3
While Loops
Loops allow continuous execution of a statement or group of statements, usually until a condition is met.

C17
#include <stdio.h>

int main() {
	int x = 1;
	while(x <= 3) {
		printf("%d\n", x++);
	}
	return 0;
}
C++20
#include <iostream>

int main() {
	auto x = 1;
	while(x <= 3) {
		std::cout << x++ << std::endl;
	}
	return 0;
}
output: 1
        2
        3
Goto
Used to jump between code sections. The use of goto is contraversial as it can promote bad code decisions, but it can be very useful for avoiding large nested ‘if’ statements.

C17
#include <stdio.h>

int main() {
	int x;
	scanf("%d", &x);
	if (x < 3) goto cleanup;
	// Program code here
	cleanup:
	return 0;
}
C++20
#include <iostream>

int main() {
	int x;
	std::cin >> x;
	if (x < 3) goto cleanup;
	// Program code here
	cleanup:
	return 0;
}
Integer Promotion
Any operand whose type ranks lower than int is temporarily promoted to int or unsigned int for comparison.

C17
#include <stdio.h>

int main() {
	char x = 'A';
	if (x < 'a') printf("Less than\n"); // x is promoted to int to compare it with the integer value of 'a'.
	else printf("Greater than or equal to\n");
	return 0;
}
C++20
#include <iostream>

int main() {
	auto x = 'A';
	if (x < 'a') std::cout << "Less than" << std::endl; // x is promoted to int to compare it with the integer value of 'a'.
	else std::cout << "Greater than or equal to" << std::endl;
	return 0;
}
output: Less than
Program Arguments
A program can optionally take a set of arguments from the user at launch.

C17
#include <stdio.h>

int main(int argc, char* argv[]) {
	for(int i = 0; i < argc; i++) {
		printf("%s\n", argv[i]);
	}
	return 0;
}
C++20
#include <iostream>

int main(int argc, char* argv[]) {
	for(auto i = 0; i < argc; i++) {
		std::cout << argv[i] << std::endl;
	}
	return 0;
}
input: ./program arg1 arg2
output: program
        arg1
        arg2
Storage Class Specifiers
Define the storage duration of an object.

C17
int main() {
	extern int a; // defined elsewhere
	static int b; // hold value between invocations
	register int c; // store in CPU register for fast access
	auto int d; // automatic duration - scope lifetime
	return 0;
}
C++20
int main() {
	extern int a; // defined elsewhere
	static int b; // hold value between invocations
	return 0;
}
Type Qualifiers
A way of expressing additional information about a value through the type system to ensure correctness in the use of the data.

C17
int main() {
	restrict int* a; // Should only be accessed from this pointer
	const int b; // Once defined, is constant and cannot be changed
	atomic int c; // Can only be modified by one thread at a time
	volatile int d; // Can be modified externally. the program will check x's value before using it, even if it hasn't been modified locally.
	return 0;
}
C++20
#include <atomic>

int main() {
	const int a = 1; // a, once defined, is constant and cannot be changed
	std::atomic<int> b; // b can only be modified by one thread at a time
	volatile int c; // c can be modified externally. the program will check x's value before using it, even if it hasn't been modified locally.
	return 0;
}
Inline Functions
Directly include the given function in the caller code sequence. This ensures that: function call overhead doesn’t occur ; overhead of push/pop variables on the stack is eliminated ; overhead of the return call is eliminated ; context-specific optimizations can be enabled at compile time.

C17
#include <stdio.h>

static inline void square(int* x) {
	*x *= *x;
	return;
}

int main() {
	int num = 5;
	square(&num);
	printf("%d\n", num);
	return 0;
}
C++20
#include <iostream>

inline void square(int& x) {
	x *= x;
	return;
}

int main() {
	int num = 5;
	square(num);
	std::cout << num << std::endl;
	return 0;
}
output: 25
Conditional If
Responsible for modifying the flow of execution in a program. Always used with a condition, which is evaluated first before executing any statement inside the body.

C17
#include <stdio.h>

int main() {
	int x = 4;
	if (!x) printf("x is 0\n"); // one line if statement
	else if (x < 0) printf("x is negative\n");
	else { // or you can use a block			
		printf("x is positive\n");
	}
	return 0;
}
C++20
#include <iostream>

int main() {
	if (int x = 4 ; !x) std::cout << "x is 0" << std::endl; // one line if statement with optional init statement before condition
	else if (x < 0) std::cout << "x is negative" << std::endl;
	else { // or you can use a block
		std::cout << "x is positive" << std::endl;
	}	
	return 0;
}
output: x is positive
Ternary Operator
A conditional operator that provides a shorter syntax for the if statement. The first operand is a boolean expression; if the expression is true then the value of the second operand is returned otherwise the value of the third operand is returned.

C17
#include <stdio.h>

int main() {
	int x = 4;
	x < 0 ? printf("x is negative\n") : printf("x is 0 or positive\n");
	return 0;
}
C++20
#include <iostream>

int main() {
	int x = 4;
	x < 0 ? std::cout << "x is negative" << std::endl : std::cout << "x is 0 or positive" << std::endl;
	return 0;
}
Address Resolution Operator
Use ‘&’ before a variable name to use it’s address in memory rather than the value stored.

C17
#include <stdio.h>

int main() {
	int x = 5;
	printf("The address of x is %p\n", (void*)&x);
	return 0;
}
C++20
#include <iostream>

int main() {
	int x = 5;
	std::cout << "The address of x is " << &x << std::endl;
	return 0;
}
output: The address of x is 0x7ffd7b254c2c
Dereference Operator
Use ‘*’ before a variable name to use the value it points to rather than the address stored.

C17
#include <stdio.h>

int main() {
	int x = 4;
	int* y = &x;
	printf("The value stored at x is %d\n", *y);
	return 0;
}
C++20
#include <iostream>

int main() {
	int x = 4;	
	int* y = &x;
	std::cout << "The value stored at x is " << *y << std::endl;
	return 0;
}
output: The value stored at x is 4
Pointers
A pointer is a variable that can hold the address of another variable. Just like regular data types, they must have their own type which refers to the type of the data at the address pointed to.

C17
#include <stdio.h>

int main() {
	int* x; // pointer to type int
	return 0;
}
C++20
#include <iostream>

int main() {
	int* x; // pointer to type int
	return 0;
}
Pointer Arithmetic
Perform integer addition or subtraction operations on pointers, taking the data type’s size into account to return the correct address of the next item.

C17
#include <stdio.h>

int main() {
	int x[5];
	int* x_ptr = &x[0];
	printf("Value of x_ptr = %p\n", (void*)x_ptr);
	printf("Value of x_ptr + 1 = %p\n", (void*)(x_ptr + 1));
	char y[5];
	char* y_ptr = &y[0];
	printf("Value of y_ptr = %p\n", (void*)y_ptr);
	printf("Value of y_ptr + 1 = %p\n", (void*)(y_ptr + 1));
	return 0;
}
C++20
#include <iostream>

int main() {
	int x[5];
	int* x_ptr = &x[0];
	std::cout << "Value of x_ptr = " << x_ptr << std::endl;
	std::cout << "Value of x_ptr + 1 = " << x_ptr + 1 << std::endl;
	char y[5];
	char* y_ptr = &y[0];
	std::cout << "Value of y_ptr = " << y_ptr << std::endl;
	std::cout << "Value of y_ptr + 1 = " << y_ptr + 1 << std::endl;
	return 0;
}
Output: Value of x_ptr = 492316
        Value of x_ptr + 1 = 492320
        Value of y_ptr = 492303
        Value of y_ptr + 1 = 492304
Structs
Structs are user defined data storage objects containing public members by default.

C17
#include <stdio.h>

struct my_struct {
	int x;
	int y;
};

int main() {
	struct my_struct object1;
	object1.x = 1;
	printf("%d\n", object1.x);
	return 0;
}
C++20
#include <iostream>

struct my_struct {
	int x;
	int y;
};

int main() {
	struct my_struct object1;
	object1.x = 1;
	std::cout << object1.x << std::endl;
	return 0;
}
output: 1
Union
A union is a special data type that can store different data types at the same memory location. You can define a union with many members, but only one member can contain a value at any given time. Unions provide an efficient way of using the same memory location for multiple purposes. A union’s size will be the size of the largest constituent type.

C17
#include <stdio.h>

union my_data {
	int i;
	float f;
	char str[20];
};
 
int main() {
	union my_data object1;        
	printf("Size of my_data union: %lu\n", sizeof(object1));
	return 0;
}
C++20
#include <iostream>

union my_data {
	int i;
	float f;
	char str[20];
};

int main() {
	union my_data object1;        
	std::cout << "Size of my_data union: " << sizeof(object1) << std::endl;
	return 0;
}
Output: Size of my_data union: 20
Input & Output
In C, interacting with the user console is made possible through the stdio.h (standard input output library) header, which contains methods for input and output. C++ provides a convenient abstraction built into the iostream header, known as streams, to perform input and output operations in sequential media such as the screen, the keyboard or a file. A stream is an entity that a program can use to either insert or extract data.

C17
#include <stdio.h>

int main() {
	int x;
	printf("Enter an integer value for x: ");
	scanf("%d", &x);
	printf("The value at x is now: %d\n", x);
	return 0;
}
C++20
#include <iostream>

int main() {
	int x;
	std::cout << "Enter an integer value for x: ";
	std::cin >> x;
	std::cout << "The value at x is now: " << x << std::endl;
	return 0;
}
output: Enter an integer value for x: 6
        The value at x is now: 6
Bitwise Operations
Bitwise operators are used to perform bit-level operations.

C17
#include <stdio.h>

int main() {
	unsigned char a = 5; // 00000101
	unsigned char b = 9; // 00001001
	printf("a & b = %d\n", a & b); // 00000001
	printf("a | b = %d\n", a | b); // 00001101
	printf("a ^ b = %d\n", a ^ b); // 00001100
	printf("~a = %d\n", a = ~a); // 11111010
	printf("b << 1 = %d\n", b << 1); // 00010010
	printf("b >> 1 = %d\n", b >> 1); // 00000100
	return 0;
}
C++20
#include <iostream>

int main() {
	unsigned char a = 5; // 00000101
	unsigned char b = 9; // 00001001
	std::cout << "a & b = " << (a & b) << std::endl; // 00000001
	std::cout << "a | b = " << (a | b) << std::endl; // 00001101
	std::cout << "a ^ b = " << (a ^ b) << std::endl; // 00001100
	std::cout << "~a = " << (~a) << std::endl; // 11111010
	std::cout << "b << 1 = " << (b << 1) << std::endl; // 00010010
	std::cout << "b >> 1 = " << (b >> 1) << std::endl; // 00000100
	return 0;
}
output: a & b = 1
        a | b = 13
        a ^ b = 12
        ~a = -6
        b << 1 = 18
        b >> 1 = 4
Typedef
Used to add an additional name to a type. Useful when working with more complex types, making them more human readable.

C17
#include <stdio.h>

typedef unsigned char byte;

int main() {
	byte b1 = 'c';
	return 0;
}
C++20
#include <iostream>

typedef unsigned char byte;

int main() {
	byte b1 = 'c';
	return 0;
}
Enumerations
A user-defined data type, used to assign names to integral constants to make a program easier to read and maintain.

C17
#include <stdio.h>

enum week {
	mon,
	tue,
	wed,
	thu,
	fri,
	sat,
	sun
};

int main() {
	for(int i = mon; i <= sun; i++)	{
		printf("%d\n", i); 
	} 
	return 0;
}
C++20
#include <iostream>

enum week {
	mon,
	tue,
	wed,
	thu,
	fri,
	sat,
	sun
};

int main() {
	for(int i = mon; i <= sun; i++)	{
		std::cout << i << std::endl; 
	} 
	return 0;
}
output: 0
        1
        2
        3
        4
        5
        6
Variadic Functions
Create a function with an arbitrary argument count for more flexibility.

C17
#include <stdio.h>
#include <stdarg.h>

int sum(int count, ...)
{
	int total, i, temp;
	total = 0;
	va_list args;
	va_start(args, count);
	for(int i = 0; i < count; i++) {
		temp = va_arg(args, int);
        	total += temp;
	}
	va_end(args);
	return total;
}

int main() {
	int numbers[3] = {5, 10, 15};
	int sum_of_numbers = sum(3, numbers[0], numbers[1], numbers[2]);
	printf("Sum of the array: %d\n", sum_of_numbers);
	return 0;
}
C++20
#include <iostream>
#include <cstdarg>

int sum(int count, ...)
{
	int total, i, temp;
	total = 0;
	va_list args;
	va_start(args, count);
	for(int i = 0; i < count; i++) {
		temp = va_arg(args, int);
        	total += temp;
	}
	va_end(args);
	return total;
}

int main() {
	int numbers[3] = {5, 10, 15};
	int sum_of_numbers = sum(3, numbers[0], numbers[1], numbers[2]);
	std::cout << "Sum of the array: " << sum_of_numbers << std::endl;
	return 0;
}
output: Sum of the array: 30
Threads
Used to execute one or more subthreads to allow for parallel processing in the same memory space, usually resulting in a performance improvement in a larger program.

C17
#include <stdio.h>
#include <threads.h>

int thread_func(void* arg) { 
	printf("Printing from Thread\n"); 
	return NULL;
} 
   
int main() { 
	thrd_t thread_id; 
	thrd_create(&thread_id, thread_func, NULL); 
	thrd_join(thread_id, NULL);  // Wait for thread to return before continuing execution
	printf("Thread returned\n"); 
	return 0;
}
C++20
#include <iostream>
#include <thread>

void thread_func() {
	std::cout << "Printing from Thread" << std::endl;
	return NULL;
}

int main() {
	std::thread thread_obj(thread_func);
	thread_obj.join();
	std::cout << "Thread returned" << std::endl;
	return 0;
}
output: Printing from Thread
        Thread returned
Mutex
Mutual exclusion functionality. Can be used to serialize access of shared variables between concurrent threads.

C17
#include <stdio.h>
#include <threads.h>

typedef struct data {
	mtx_t mtx;
	int x;
} data;

int thread_func(void* arg) { 
	data* d = (data*)arg;
	mtx_lock(&d->mtx);	
	d->x = 2;	
	mtx_unlock(&d->mtx);
	return 0;
} 
   
int main() {
	data d;
	mtx_init(&d.mtx, mtx_plain);
	thrd_t thread_id; 
	thrd_create(&thread_id, thread_func, (void*)&d); 
	thrd_join(thread_id, NULL);  // Wait for thread to return before continuing execution
	printf("x has safely been modified to %d\n", d.x); 
	return 0;
}
C++20
#include <iostream>
#include <thread>
#include <mutex>

typedef struct data {
	std::mutex mtx;
	int x;
} data;

void thread_func(data* d) { 
	d->mtx.lock()
	d->x = 2;	
	d->mtx.unlock()
	return;
} 
   
int main() {
	data d;
	std::thread thread_obj(thread_func, &d); 
	thread_obj.join();  // Wait for thread to return before continuing execution
	std::cout << "x has safely been modified to " << d.x << std::endl; 
	return 0;
}
Heap Allocation
Memory can be allocated on the heap, an unreserved and relatively large region of memory outside of the program’s memory scope.

C17
#include <stdio.h>
#include <stdlib.h>

int main() {
	int* x = (int*)malloc(sizeof(int)); // pointer to a heap-reserved integer
	if (x) { // test that the memory was allocated before you use it
		free(x); // you must manually free any memory you allocated on the heap or it will persist (memory leak)
	}
	return 0;
}
C++20
#include <iostream>

int main() {
	int* p  = new(int); // pointer to a heap-reserved integer
	if (p != nullptr) { // test that the memory was allocated before you use it
		delete p; // you must manually free any memory you allocated on the heap or it will persist (memory leak)
	}
	return 0;
}
Assertions
Statements used to explicitly test assumptions made by the programmer. Will be checked at runtime, or if static at compile time. A powerful tool for statement or unit testing.

C17
#include <stdio.h>
#include <assert.h>

int main() {
	int x = 1;
	assert(x == 2); // this should break the execution of the program
	return 0;
}
C++20
#include <assert.h>

int main() {
	int x = 1;
	assert(x == 2); // this should break the execution of the program
	return 0;
}
output: int main(): Assertion `x == 2' failed. 
Compound Assignment
Provides a shorter syntax for assigning the result of an arithmetic or bitwise operator by performing an operation on the two operands before assigning the result to the first operand.

C17
#include <stdio.h>

int main() {
	int x = 1;
	x += 1;
	printf("x = %d\n", x);
	return 0;
}
C++20
#include <iostream>

int main() {
	int x = 1;
	x += 1;
	std::cout << "x = " << x << std::endl;
	return 0;
}
output: x = 2
Project Structure
It’s useful to follow a conventional and sensible structure when organizing a project, to maintain readability.

C17
myproject/src/main.c // main function
myproject/include/file.c // function definitions etc
myproject/include/file.h // structs, function prototypes etc
myproject/Makefile // automated project build file
myproject/README.md // store any useful documentation or links to documentation in here
myproject/obj/file // temporary object files
myproject/bin/file // executable output from compiler
C++20
myproject/src/main.cpp // main function
myproject/include/file.cpp // function definitions etc
myproject/include/file.hpp // classes, function prototypes etc
myproject/Makefile // automated project build file
myproject/README.md // store any useful documentation or links to documentation in here
myproject/obj/file // temporary object files
myprobect/bin/file // executable output from compiler
Includes
Includes are instructions to the preprocessor to include external code. External code is made up of at least a header file (interface) and a source file (implementation).

When compiling your program, #include the header, and link the source file at compile time.

C17
In file src/main.c

#include <stdio.h> // Include a dependency from the system library
#include "../include/file.h" // Include a local dependency from a relative path

int main() {
	// Use file.h
}
In file include/file.c:

#include <stdio.h> // Include a dependency from the system library
#include "file.h" // Include a local dependency from a relative path
In file include/file.h:

#ifndef PROG_H // Only process the below if it hasn't already been processed in the current compilation.
#define PROG_H

// File contents here

#endif
C++20
In file src/main.cpp

#include <iostream> // Include a dependency from the system library
#include "../include/file.hpp" // Include a local dependency from a relative path

int main() {
	// Use file.hpp
}
In file include/file.cpp:

#include <iostream> // Include a dependency from the system library
#include "file.hpp" // Include a local dependency from a relative path
In file include/file.hpp:

#ifndef PROG_HPP // Only process the below if it hasn't already been processed in the current compilation.
#define PROG_HPP

// File contents here

#endif
Compilation
Compiling source code turns it into machine language through preprocessing, compiling, assembly and linking.

C17
gcc -c -std=c17 src/main.c -o obj/main.o // Compile main.c to object
gcc -c -std=c17 include/file.c -o obj/file.o // Compile file.c to object
gcc obj/main.o obj/file.o -o bin/prog // Link objects and create executable bin/prog
C++20
g++ -c -std=c++20 src/main.cpp -o obj/main.o // Compile main.cpp to object
g++ -c -std=c++20 include/file.cpp -o obj/file.o // Compile file.cpp to object
g++ obj/main.o obj/file.o -o bin/prog // Link objects and create executable bin/prog
Modules
Modules are a new method in C++ to allow for better package management and easier library integration.

C++20
In file foo.cpp:

export module Foo;

namespace Bar {
	int f_internal() {
	        return 10;
	}

	export int f() {
		return f_internal();
	}
}
In file main.cpp:

import std;
import Foo;

int main() {
	std::cout << Bar::f() << std::endl;
	return 0;
}
output: 10
Pass by Reference
Use the & symbol as an alternative to passing an address by pointer or passing by value.

C++20
#include <iostream>

void square(int& x) {
	x *= x;
	return;
}

int main() {
	int x = 2;
	square(x);
	std::cout << x << std::endl;
	return 0;
}
output: 4
Range
Used as a more readable equivalent to a traditional loop when iterating over a range of data.

C++20
#include <iostream>
#include <vector>
 
int main() {
	std::vector<int> v = {0, 1, 2, 3};
	for(const int& i : v) { // access using const reference
		std::cout << i << std::endl;
	}
	int a[] = {4, 5, 6, 7};
	for(int n : a) { // the initializer can be an array
		std::cout << n << std::endl;
	}
	return 0;
}
output: 0
        1
        2
        3
        4
        5
        6
        7
Namespaces
A declarative region that provides a named scope to its constituent identifiers. Useful for organizing and reducing ambiguity in code. The scope resolution operator :: is used to access a scope’s contents.

C++20
#include <iostream>

namespace ns_1 {
	void func() {
		std::cout << "Called from ns_1" << std::endl;
	}
}

namespace ns_2 {
	void func() {
		std::cout << "Called from ns_2" << std::endl;
	}
}

int main () {
	ns_1::func();
	ns_2::func(); 
	return 0;
}
output: Called from ns_1
        Called from ns_2
Classes
A user-defined data structure template declared with keyword class containing member functions and data.

C++20
#include <iostream>

class human {
public:
	int height;
	int weight;
};

int main() {
	human john;
	john.height = 180;
	john.weight = 220;
	return 0;
}
Class Methods
Functions of a class.

C++20
#include <iostream>

class human {
public:
	int height;
	int weight;
	int get_height() const {
		return height;
	}
	int get_weight() const {
		return weight;
	}
};

int main() {
	human john;
	john.height = 180;
	john.weight = 220;
	std::cout << john.get_height() << std::endl;
	std::cout << john.get_weight() << std::endl;
	return 0;
}
output: 180
        220
Constructors & Destructors
A constructor is an optional special member function of a class used to instantiate the class object. It must take the same name as the class, with no return type. A destructor is an optional special member function of a class called in the destruction of a class object. It must take the same name as the class, preceded with ~, and with no return type.

C++20
#include <iostream>

class human {
public:
	int height;
	int weight;
	human(int h, int w) {
		height = h;
		weight = w;
	}
	~human(){};
	int get_height() const {
		return height;
	}
	int get_weight() const {
		return weight;
	}
};

int main() {
	human john(180, 220);
	std::cout << john.get_height() << std::endl;
	std::cout << john.get_weight() << std::endl;
	return 0;
}
output: 180
        220
Encapsulation
Fundamental OOP concept used to group together data and functions, and provide varying levels of abstraction from the user.

C++20
#include <iostream>

class human {
private: // abstracted from the user
	int height;
	int weight;
public: 
	human(int h, int w) {
		height = h;
		weight = w;
	}
	int get_height() const {
		return height;
	}
	int get_weight() const {
		return weight;
	}
};

int main() {
	human john(180, 220);
	std::cout << john.get_height() << std::endl;
	std::cout << john.get_weight() << std::endl;
	return 0;
}
output: 180
        220
Inheritance
Fundamental OOP concept. The capability of a class to derive properties and characteristics from another class.

C++20
#include <iostream>

class human {
public:
	int height;
	int weight;
public: 
	human(int h, int w) {
		height = h;
		weight = w;
	}
	int get_height() const {
		return height;
	}
	int get_weight() const {
		return weight;
	}
};

class adult : public human { // inherit from human class
public:
    adult(int h, int w) : human(h, w) {} // call the base class constructor from this constructor
    std::string occupation;
	std::string get_occupation() const {
		return occupation;
	}	
};

int main() {
	adult john(180, 220);
	john.occupation = "lawyer";
	std::cout << john.get_height() << std::endl;
	std::cout << john.get_weight() << std::endl;
	std::cout << john.get_occupation() << std::endl;
	return 0;
}
output: 180
        220
        lawyer
Polymorphism
Fundamental OOP concept. Allows operations or objects to behave differently in different contexts.

Function Overloading
Used to facilitate compile-time polymorphism by allowing creation of more than one function with the same name but with different parameters.

C++20
#include <iostream>

class human {
public:
	int height;
	float weight;
	human(int h, int w) {
		height = h;
		weight = w;
	}
};

int print(int x) {
	std::cout << x << std::endl;
}

int print(float x) {
	std::cout << x  << std::endl;
}

int main() {
	human john(180, 220);
	print(john.height);
	print(john.weight);
	return 0;
}
output: 180
        220
Virtual Functions
Used to facilitate runtime polymorphism by allowing redefinition of a base class function.

C++20
#include <iostream>

class human {
public:
	int height;
	int weight;
public: 
	human(int h, int w) {
		height = h;
		weight = w;
	}
	int get_height() const {
		return height;
	}
	int get_weight() const {
		return weight;
	}
	virtual void print_all() = 0; // ()=0 creates a _pure_ virtual function that must be overridden. Alternatively you can just write a default function as a virtual function with no requirement to be overwritten.
};

class adult : public human { // inherit from human class
public:
    adult(int h, int w) : human(h, w) {}
    std::string occupation;
	std::string get_occupation() const {
		return occupation;
	}	
	void print_all() { // virtual function overridden in derived class
		std::cout << height << std::endl;
		std::cout << weight << std::endl;
		std::cout << occupation << std::endl;
	}
};

int main() {
	adult john(180, 220);
	john.occupation = "lawyer";
	john.print_all();
	return 0;
}
output: 180
        220
        lawyer
Friend Functions
A function of a class defined outside of its scope but with the right to access all private and protected members of the class.

C++20
#include <iostream>

class human {
private:
	int weight;
public:
	human(int w) {
		weight = w;	    
	}
	friend int get_weight(human h);
};

int get_weight(human h) {
	return h.weight; // we can access the private members of the associated class thanks to the friend function
}

int main() {
	human john(220);
	std::cout << get_weight(john) << std::endl;
	return 0;
}
output: 220
Templates
A blueprint for creating a generic class or function. The foundation of generic programming, which involves writing code in a way that is independent of any particular type.

C++20
#include <iostream>

template <class T>
T largest(T n1, T n1) {
	return (n1 > n2) ? n1 : n2;
}

int main() {
	int x, y;
	std::cout << "Enter two integers: " << std::endl;
	std::cin >> x >> y;
	std::cout << largest(x, y) << std::endl;
	return 0;
}
input:  2
        5
output: 5
Structured Bindings
A convenient way to declare multiple variables initialized from a tuple, pair or struct. Often used to capture multiple return values from a function.

C++20
#include <iostream>
  
struct Point {
    int x;
    int y;
};
  
int main() {
    Point p = {1, 2};
    auto[x, y] = p; // Creates and initializes x and y variables
    std::cout << x << std::endl;
    std::cout << y << std::endl;     
    return 0;
}
output: 1
        2
Lambda Expressions
Also referred to as Lambda Functions. A simplified notation for defining and using an anonymous function object, capable of capturing variables in scope.

C++20
#include <iostream>

int main() {
	int x = 1;
	auto multiply = [&x](int y)->int{ // Anonymous function takes a reference to x. Returns an int
		return x*y;
	};
	std::cout << multiply(5) << std::endl;
	x = 2;
	std::cout << multiply(5) << std::endl;
	return 0;
}
output: 5
        10
Exception Handling
A mechanism to handle runtime errors by transferring control from one part of a program to another.

C++20
#include <iostream>

double divide(double dividend, double divisor) {
    if (divisor == 0) {
            throw "Cannot divide by 0\n"; // If divisor is 0, throw this error
    }
    return dividend / divisor;
}

int main() {
    try {
        std::cout << divide(10, 0) << std::endl;

    } catch (const char *err) {
        std::cout << err << std::endl;
    }
    return 0;
}
output: Cannot divide by 0