Output with printf

Let's start with one of the most important operations in C: output. C uses the printf() function to print text. To display Hello World!, write:

printf("Hello World!");

This prints Hello World! in the terminal or Command Prompt.

Headers and the main function

Header files are another important part of C programming. Examples include <stdio.h> and <math.h>, which provide declarations for standard-library features. For the input and output examples in this series, include <stdio.h> with #include <stdio.h>.

The program also has a main function, int main() {}. The statements inside its braces are executed when the program runs. After completing its work, the main function can return 0 with return 0;.

Think of a semicolon, ;, as the period at the end of a statement. Remember to include it where a statement requires one.

Editorial note: the original introduction described <stdio.h> as necessary for every C program. It is needed for the standard input/output functions used here, not for every possible C program.

Line breaks

The escape sequence \n inserts a newline, similar to pressing Enter when typing text.

printf("Hello World!\n");

Let's add another sentence:

printf("Hello World!\n Welcome!");

The terminal displays Hello World! on the first line and Welcome! on the next. The space before Welcome! in this particular string is also printed.

You can separate the two messages into two calls to make the code easier to read:

printf("Hello World!\n");
printf("Welcome!");

You still need \n: writing two printf() statements on separate source-code lines does not automatically insert a line break into their output.

Complete examples

#include <stdio.h>

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

#include <stdio.h>

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