C Functions
C functions are fundamental building blocks in C programming. They encapsulate a set of instructions that perform a specific task and can be reused throughout your code.
One of their key features is the ability to accept data from the outside world through parameters.
Functions are used to perform certain actions, and they are important for reusing code: Define the code once, and use it many times.
Predefined Functions
Predefined functions, also known as library functions or standard library functions, are a set of functions readily available for use in your C programs. They are pre-written and compiled, saving you the time and effort of implementing them yourself. These functions come from standard C libraries like stdio.h, math.h, string.h, and more.
For example, main() is a function, which is used to execute code, and printf() is a function; used to output/print text to the screen:
Example
#include <stdio.h>
int main() {
printf("Hello CodeLines!");
return 0;
}
Optput
CodeLines
Create a Function
To create (often referred to as declare) your own function, specify the name of the function, followed by parentheses () and curly brackets {}:
Example
void myFunction() {
// code to be executed
}
Example Explained
myFundanction() is the name of the function
void means that the function does not have a return value. You will learn more about return values later in the next chapter
Inside the function (the body), add code that defines what the function should do
Call a Function
Declared functions are not executed immediately. They are "saved for later use", and will be executed when they are called.
To call a function, write the function's name followed by two parentheses () and a semicolon ;
In the following example, myFunction() is used to print a text (the action), when it is called:
Example
Inside main, call myFunction():
#include <stdio.h>
int main() {
// Create a function
void myFunction() {
printf("I just got executed!");
}
int main() {
myFunction(); // call the function
return 0;
}
Optput
I just got executed!
A function can be called multiple times:
Example
#include <stdio.h>
int main() {
// Create a function
void myFunction() {
printf("I just got executed!\n");
}
int main() {
myFunction(); // call the function
myFunction(); // call the function
myFunction(); // call the function
return 0;
}
Optput
I just got executed!
I just got executed!
I just got executed!