Example: General Time Calculator (Total Minutes) in C

// General Time Calculator (Total Minutes)
#include <stdio.h>

// Function to convert hours and minutes to total minutes
int toTotalMinutes(int hours, int minutes) {
    return hours * 60 + minutes;
}

// Function to convert total minutes back to hours and minutes
void fromTotalMinutes(int totalMinutes, int *hours, int *minutes) {
    *hours = totalMinutes / 60;
    *minutes = totalMinutes % 60;
}

int main() {
    // Step 1: Declare variables for input and intermediate total minutes
    int h1, m1, h2, m2;
    int total_min1, total_min2, result_total_minutes;
    int result_h, result_m;
    char operation;

    // Step 2: Get first time duration
    printf("Enter first duration (hours minutes): ");
    scanf("%d %d", &h1, &m1);
    total_min1 = toTotalMinutes(h1, m1);

    // Step 3: Get operation (+ or -)
    printf("Enter operation (+ or -): ");
    scanf(" %c", &operation); // Note the space before %c to consume newline

    // Step 4: Get second time duration
    printf("Enter second duration (hours minutes): ");
    scanf("%d %d", &h2, &m2);
    total_min2 = toTotalMinutes(h2, m2);

    // Step 5: Perform calculation based on operation
    if (operation == '+') {
        result_total_minutes = total_min1 + total_min2;
        printf("Result of addition: ");
    } else if (operation == '-') {
        result_total_minutes = total_min1 - total_min2;
        // Ensure non-negative result for simplicity, or handle negative as duration
        if (result_total_minutes < 0) {
            printf("Result is negative (second duration was larger). Absolute difference: ");
            result_total_minutes = -result_total_minutes;
        } else {
            printf("Result of subtraction: ");
        }
    } else {
        printf("Invalid operation.\n");
        return 1; // Indicate an error
    }

    // Step 6: Convert result back to hours and minutes
    fromTotalMinutes(result_total_minutes, &result_h, &result_m);

    // Step 7: Print the final result
    printf("%d hours %d minutes\n", result_h, result_m);

    return 0;
}