8. Function Examples and Applications

8.1 Menu-Driven Program

#include <stdio.h>

// Function prototypes
void display_menu(void);
int get_choice(void);
void calculator_add(void);
void calculator_multiply(void);
void display_table(int num);

int main() {
    int choice;
    
    do {
        display_menu();
        choice = get_choice();
        
        switch (choice) {
            case 1:
                calculator_add();
                break;
            case 2:
                calculator_multiply();
                break;
            case 3:
                printf("Enter number for multiplication table: ");
                int num;
                scanf("%d", &num);
                display_table(num);
                break;
            case 4:
                printf("Thank you for using the calculator!\n");
                break;
            default:
                printf("Invalid choice! Please try again.\n");
        }
        
        if (choice != 4) {
            printf("\nPress Enter to continue...");
            getchar();
            getchar();  // Clear buffer
        }
        
    } while (choice != 4);
    
    return 0;
}

void display_menu(void) {
    printf("\n=== SIMPLE CALCULATOR ===\n");
    printf("1. Addition\n");
    printf("2. Multiplication\n");
    printf("3. Multiplication Table\n");
    printf("4. Exit\n");
    printf("========================\n");
}

int get_choice(void) {
    int choice;
    printf("Enter your choice (1-4): ");
    scanf("%d", &choice);
    return choice;
}

void calculator_add(void) {
    float num1, num2;
    printf("Enter first number: ");
    scanf("%f", &num1);
    printf("Enter second number: ");
    scanf("%f", &num2);
    printf("Result: %.2f + %.2f = %.2f\n", num1, num2, num1 + num2);
}

void calculator_multiply(void) {
    float num1, num2;
    printf("Enter first number: ");
    scanf("%f", &num1);
    printf("Enter second number: ");
    scanf("%f", &num2);
    printf("Result: %.2f × %.2f = %.2f\n", num1, num2, num1 * num2);
}

void display_table(int num) {
    printf("\nMultiplication table for %d:\n", num);
    printf("-------------------------\n");
    for (int i = 1; i <= 10; i++) {
        printf("%d × %d = %d\n", num, i, num * i);
    }
}

8.2 Temperature Conversion Program

#include <stdio.h>

// Function prototypes
float celsius_to_fahrenheit(float celsius);
float fahrenheit_to_celsius(float fahrenheit);
float celsius_to_kelvin(float celsius);
float kelvin_to_celsius(float kelvin);
void display_conversion_table(void);

int main() {
    int choice;
    float temp, result;
    
    printf("=== TEMPERATURE CONVERTER ===\n");
    printf("1. Celsius to Fahrenheit\n");
    printf("2. Fahrenheit to Celsius\n");
    printf("3. Celsius to Kelvin\n");
    printf("4. Kelvin to Celsius\n");
    printf("5. Display Conversion Table\n");
    printf("============================\n");
    
    printf("Enter choice (1-5): ");
    scanf("%d", &choice);
    
    switch (choice) {
        case 1:
            printf("Enter temperature in Celsius: ");
            scanf("%f", &temp);
            result = celsius_to_fahrenheit(temp);
            printf("%.2f°C = %.2f°F\n", temp, result);
            break;
            
        case 2:
            printf("Enter temperature in Fahrenheit: ");
            scanf("%f", &temp);
            result = fahrenheit_to_celsius(temp);
            printf("%.2f°F = %.2f°C\n", temp, result);
            break;
            
        case 3:
            printf("Enter temperature in Celsius: ");
            scanf("%f", &temp);
            result = celsius_to_kelvin(temp);
            printf("%.2f°C = %.2fK\n", temp, result);
            break;
            
        case 4:
            printf("Enter temperature in Kelvin: ");
            scanf("%f", &temp);
            if (temp < 0) {
                printf("Error: Temperature cannot be below 0 Kelvin!\n");
            } else {
                result = kelvin_to_celsius(temp);
                printf("%.2fK = %.2f°C\n", temp, result);
            }
            break;
            
        case 5:
            display_conversion_table();
            break;
            
        default:
            printf("Invalid choice!\n");
    }
    
    return 0;
}

float celsius_to_fahrenheit(float celsius) {
    return (celsius * 9.0 / 5.0) + 32.0;
}

float fahrenheit_to_celsius(float fahrenheit) {
    return (fahrenheit - 32.0) * 5.0 / 9.0;
}

float celsius_to_kelvin(float celsius) {
    return celsius + 273.15;
}

float kelvin_to_celsius(float kelvin) {
    return kelvin - 273.15;
}

void display_conversion_table(void) {
    printf("\n=== TEMPERATURE CONVERSION TABLE ===\n");
    printf("Celsius  | Fahrenheit | Kelvin\n");
    printf("---------+------------+--------\n");
    
    for (int c = 0; c <= 100; c += 10) {
        float f = celsius_to_fahrenheit(c);
        float k = celsius_to_kelvin(c);
        printf("%8d | %10.1f | %6.1f\n", c, f, k);
    }
}