Defining functions
- C course
- Beginner
- Lesson 65/116
- 4 min
Learn how to define and call a function.
What is a function?
A function is a named, reusable block of code. The void return type means the function returns no value.
void greet(void) {
printf("Hello!\n");
}
int main(void) {
greet();
return 0;
}Defining a function does not run it; it only runs when called (greet();). This keeps code organized and free of repetition.
Calling a function
You call a function by its name with parentheses: greet();. The parentheses signal a function call.
void write(void) {
printf("Line 1\n");
printf("Line 2\n");
}
int main(void) {
write(); /* prints two lines */
write(); /* prints again */
return 0;
}You can call the same function multiple times; this avoids code duplication. main is also a function, and it is the first one called when the program starts.
Practice Define and call the greet function
Define void greet(void) with the body printf("Hello!\n");. Call greet() from main. Output should be Hello!.
Starter code
#include <stdio.h>
/* define greet function */
int main(void) {
/* call greet */
return 0;
}Sample solution
#include <stdio.h>
void greet(void) {
printf("Hello!\n");
}
int main(void) {
greet();
return 0;
}Expected output
Hello!
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Which of the following is a function definition?
- greet();
- void greet(void) { ... } Correct answer
- int x = 5;
- return 0;
Explanation: Return type, name and parentheses form a function definition.
2 Function body
void greet(void) ____ printf("Hello\n");
}void greet(void) { printf("Hello\n");
}Explanation: The body goes between curly braces.
3 Match function parts
| Term | Meaning |
|---|---|
void |
return type |
greet |
function name |
(void) |
parameter |
{ } |
body |