Example: Internet Billing Calculator in C

// Internet Billing Calculator
#include <stdio.h>

int main() {
    // Step 1: Declare variables for plan details and customer usage
    float baseCost;           // Base cost of the internet plan
    int dataLimitGB;          // Data limit included in the base plan (in GB)
    float overageRatePerGB;   // Cost per GB for data exceeding the limit
    int monthlyUsageGB;       // Customer's actual monthly data usage (in GB)
    float totalBill;          // Calculated total monthly bill

    // Step 2: Get plan details from the user
    printf("--- Internet Billing Plan Setup ---\n");
    printf("Enter base monthly cost of the plan: $");
    scanf("%f", &baseCost);

    printf("Enter data limit included in plan (in GB): ");
    scanf("%d", &dataLimitGB);

    printf("Enter overage rate per GB (e.g., 1.50 for $1.50/GB): $");
    scanf("%f", &overageRatePerGB);

    // Step 3: Get customer's monthly data usage
    printf("\n--- Customer Usage Input ---\n");
    printf("Enter customer's monthly data usage (in GB): ");
    scanf("%d", &monthlyUsageGB);

    // Step 4: Calculate the total bill based on usage
    if (monthlyUsageGB <= dataLimitGB) {
        // If usage is within the limit, bill is just the base cost
        totalBill = baseCost;
        printf("\nUsage is within the %.0d GB limit.\n", dataLimitGB);
    } else {
        // If usage exceeds the limit, calculate overage charges
        int overageGB = monthlyUsageGB - dataLimitGB;
        float overageCharge = overageGB * overageRatePerGB;
        totalBill = baseCost + overageCharge;
        printf("\nUsage exceeded the limit by %d GB.\n", overageGB);
        printf("Overage charge: $%.2f\n", overageCharge);
    }

    // Step 5: Display the total monthly bill
    printf("----------------------------------\n");
    printf("Base Plan Cost:           $%.2f\n", baseCost);
    printf("Monthly Data Usage:       %d GB\n", monthlyUsageGB);
    printf("Total Monthly Bill:       $%.2f\n", totalBill);
    printf("----------------------------------\n");

    return 0;
}