Program Structure

Consider the following hello world program, hello.cpp:


int main(){
    std::cout << "Hello World" << std::endl; 
    return 0;

The program runs from top to bottom, line by line:

  • The first line instructs the compiler to locate the file that contains a library called iostream.
    • This library contains code that allows for I/O (input & output).
  • The main() function houses all the instructions for the program.

Basic Output

Now let's talk more about the std::cout in our program above. This is used to display output to the user's command line or terminal. To use std::cout, you must use it following << and a string or variable you wish to output.

std::cout << "The answer of the test is: " << answer << std::endl;

Note: std::endl is used to end the line of the output.


Comments are useful to document code, temporary debugging and in C++, it supports two different type of comments, single line // and multi-line /* */. Comments are ignored by the compiler at compiler time, making them a very good way to organize your code.

// This single line will be ignored

The first C++ program written by MKProjects 
was only available for Linux on Sanp!
All of this will be ignored !!!

Compile and Run

Since we have our program, hello.cpp, we may as well compile and run it.

# First compile the program with g++ 
$ g++ hello.cpp

# Now run the binary to execute the program 
$ ls
a.out hello.cpp

$ ./a.out 
Hello World