Defining and Calling Functions

Anatomy

int add(int a, int b) {      // return type, name, parameters
    return a + b;            // body: compute and return
}

int sum = add(2, 3);         // call: arguments 2 and 3

A function packages a computation under a name. Define it once, call it many times. void means "returns nothing":

void greet(const char* name) {
    printf("Hello, %s!\n", name);
    return;                   // optional for void
}

Why functions

• Name the idea — is_leap(y) reads better than a wall of conditions.
• Test in isolation — a pure function is trivially testable (our whole grading model depends on this).
• One responsibility — if you can't name it in a few words, split it.

Execution

A call jumps to the body, runs it, and resumes right after the call site, carrying the return value. Arguments are copies (module 11 shows how to let a function modify the caller's variables).