A function is a block of code which only runs when it is called. You can pass data, known as parameters, into a function. 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
So it turns out you already know what a function is. You have been using it the whole time while studying this tutorial!
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
int main() {printf(“Hello World!”);
return 0;
}