Your first program

Learn to write your first C program with the main function, #include and printf.

main and printf

Every C program starts from the main function. The #include <stdio.h> line brings in the printf declaration so you can print text.

#include <stdio.h>

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

Here int is the return type, main is the entry point, void means no parameters. printf writes text, return 0; signals success.

What does return 0 mean?

The return 0; statement at the end of main tells the operating system the program finished successfully. A non-zero value usually signals an error.

In modern C, writing return 0; in main is common. Other functions return whatever value they compute.

Exercise Write your first C program

Write a C program. Start with #include <stdio.h>, define int main(void), and print Hello with printf.

Show example solution

#include <stdio.h>

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

Test yourself

What does #include <stdio.h> do?
- Defines a class
- Brings in the printf declaration
- Declares a variable
- Defines the main function
Show answer

Brings in the printf declaration — #include <stdio.h> includes the stdio header, which declares printf.
Complete the printf call
```
printf(____);
```
Show answer
```
printf("Hello");
```
Match the keywords

#include

Import
int

Integer type
main

Entry point
printf

Output

Next lesson: Compile and run

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