User Defined Functions (C)¶

Learning Objectives¶

Write and call C functions with/without arguments and return values.
Use functions from main() and from another function.
Implement recursive functions.

Function Types¶

No arguments, no return value.
No arguments, return value.
With arguments, no return value.
With arguments, return value.

C Example¶

#include <stdio.h>

void greet(void) {
    printf("Welcome\n");
}

int readNumber(void) {
    int n;
    scanf("%d", &n);
    return n;
}

void printSquare(int n) {
    printf("Square: %d\n", n * n);
}

int add(int a, int b) {
    return a + b;
}

int fact(int n) {
    if (n <= 1) return 1;
    return n * fact(n - 1);
}

int main(void) {
    greet();
    printf("Enter number: ");
    int x = readNumber();
    printSquare(x);
    printf("Sum(5,7) = %d\n", add(5, 7));
    printf("fact(5) = %d\n", fact(5));
    return 0;
}

Dry Run (Recursion)¶

fact(5) -> 5*fact(4) -> 5*4*fact(3) -> ... -> 5*4*3*2*1 = 120.

Common Mistakes¶

Missing function prototype (in older C flow).
Wrong return type.
Infinite recursion (no base condition).

Practice¶

Create max-of-two function.
Create sum-of-array function.
Write recursive Fibonacci.