C Programs Using Functions

Here are some C programs that utilize functions for various purposes:

1. Calculator Program:

#include <stdio.h>

// Function to add two numbers
double add(double a, double b) {
    return a + b;
}

// Function to subtract two numbers
double subtract(double a, double b) {
    return a - b;
}

// Function to multiply two numbers
double multiply(double a, double b) {
    return a * b;
}

// Function to divide two numbers
double divide(double a, double b) {
    if (b != 0) {
        return a / b;
    } else {
        printf("Error: Division by zero\n");
        return 0;
    }
}

int main() {
    char operator;
    double num1, num2, result;

    printf("Enter an operator (+, -, *, /): ");
    scanf(" %c", &operator);

    printf("Enter two numbers: ");
    scanf("%lf %lf", &num1, &num2);

    switch (operator) {
        case '+':
            result = add(num1, num2);
            break;
        case '-':
            result = subtract(num1, num2);
            break;
        case '*':
            result = multiply(num1, num2);
            break;
        case '/':
            result = divide(num1, num2);
            break;
        default:
            printf("Error: Invalid operator\n");
            return 1;
    }

    printf("Result: %lf\n", result);
    return 0;
}
    

2. Fibonacci Series:

#include <stdio.h>

// Recursive function to generate Fibonacci series
int fibonacci(int n) {
    if (n <= 1) {
        return n;
    } else {
        return fibonacci(n - 1) + fibonacci(n - 2);
    }
}

int main() {
    int n, i;

    printf("Enter the number of terms: ");
    scanf("%d", &n);

    printf("Fibonacci Series:\n");
    for (i = 0; i < n; i++) {
        printf("%d ", fibonacci(i));
    }

    return 0;
}
    

3. Factorial Calculation:

#include <stdio.h>

// Recursive function to calculate factorial
int factorial(int n) {
    if (n <= 1) {
        return 1;
    } else {
        return n * factorial(n - 1);
    }
}

int main() {
    int num;

    printf("Enter a positive integer: ");
    scanf("%d", &num);

    if (num < 0) {
        printf("Error: Factorial is defined for non-negative integers.\n");
    } else {
        int fact = factorial(num);
        printf("Factorial of %d is %d\n", num, fact);
    }

    return 0;
}