Lesson 2: Hello World

Write your first C program, Hello World. A clear walkthrough of the compile and run flow.

The Most Basic Program — Hello World

When learning programming, the first thing you write is Hello World. It contains every essential element of the C language in one tiny program.

#include<stdio.h>

int main(void){
  printf("Hello World!\n");
  return 0;
}

Output

Hello World!

Click each line to see its explanation.

#include<stdio.h>
int main(void){
  printf("Hello World!\n");
  return 0;
}

↑ Click any line above to see its explanation.

Change the text inside printf("...") and display your own message.

my_hello.c

Output

Click "Run" to execute...

Check your understanding of this lesson!

start()

main()

init()

In C, the main() function is the entry point (starting point) of the program.

Hello (with newline)

Hello (no newline)

Error

printf does not add a newline unless you include \n. To add a newline, write printf("Hello\n");.

Runs the program

Imports the standard I/O library

Declares a variable

stdio.h is the Standard I/O header file, required for using functions like printf and scanf.

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