C语言基础菜单驱动无全局变量汽油费用计算器作业技术咨询

Got it, let's refactor your existing code into a clean, menu-driven C program that eliminates global variables entirely. Global variables can make code harder to debug and maintain, so replacing them with local variables and structured data is a great move for a course project.

Key Improvements We'll Make #

• Replace global variables with a struct to group related data (mileage, price per gallon, MPG, total cost)
• Build a simple text-based menu for user interaction
• Split functionality into modular functions that accept parameters instead of relying on globals
• Add input validation to handle invalid user entries (a nice touch for robustness)

Complete Refactored Code #

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>

// Struct to hold all calculator data (no globals needed!)
typedef struct {
    float currentMileage;
    float pricePerGallon;
    float MPG;
    float totalCost;
} GasCalculator;

// Function prototypes
void displayMenu();
void inputMileage(GasCalculator *calc);
void inputPricePerGallon(GasCalculator *calc);
void inputMPG(GasCalculator *calc);
void calculateTotalCost(GasCalculator *calc);
void displayResults(GasCalculator *calc);
void clearScreen();
void pauseProgram();

int main() {
    GasCalculator calc = {0.0, 0.0, 0.0, 0.0}; // Initialize all values to 0
    int choice;

    do {
        clearScreen();
        displayMenu();
        printf("Enter your choice: ");
        // Input validation for menu choice
        while (scanf("%d", &choice) != 1 || choice < 1 || choice > 6) {
            printf("Invalid input! Please enter a number between 1 and 6: ");
            // Clear invalid input from buffer
            while (getchar() != '\n');
        }

        switch(choice) {
            case 1:
                inputMileage(&calc);
                break;
            case 2:
                inputPricePerGallon(&calc);
                break;
            case 3:
                inputMPG(&calc);
                break;
            case 4:
                calculateTotalCost(&calc);
                printf("Total cost calculated successfully!\n");
                pauseProgram();
                break;
            case 5:
                displayResults(&calc);
                pauseProgram();
                break;
            case 6:
                printf("Exiting program...\n");
                break;
            default:
                printf("Invalid choice! Please try again.\n");
                pauseProgram();
        }
    } while (choice != 6);

    return 0;
}

void displayMenu() {
    printf("=== Gas Cost Calculator Menu ===\n");
    printf("1. Enter Current Mileage\n");
    printf("2. Enter Price Per Gallon\n");
    printf("3. Enter MPG (Miles Per Gallon)\n");
    printf("4. Calculate Total Gas Cost\n");
    printf("5. Display Results\n");
    printf("6. Exit\n");
    printf("===============================\n");
}

void inputMileage(GasCalculator *calc) {
    clearScreen();
    printf("Enter current mileage (miles): ");
    // Input validation for positive float
    while (scanf("%f", &calc->currentMileage) != 1 || calc->currentMileage < 0) {
        printf("Invalid input! Please enter a non-negative number: ");
        while (getchar() != '\n');
    }
    printf("Mileage set to %.2f miles\n", calc->currentMileage);
}

void inputPricePerGallon(GasCalculator *calc) {
    clearScreen();
    printf("Enter price per gallon ($): ");
    while (scanf("%f", &calc->pricePerGallon) != 1 || calc->pricePerGallon < 0) {
        printf("Invalid input! Please enter a non-negative number: ");
        while (getchar() != '\n');
    }
    printf("Price per gallon set to $%.2f\n", calc->pricePerGallon);
}

void inputMPG(GasCalculator *calc) {
    clearScreen();
    printf("Enter MPG (miles per gallon): ");
    while (scanf("%f", &calc->MPG) != 1 || calc->MPG <= 0) {
        printf("Invalid input! Please enter a positive number: ");
        while (getchar() != '\n');
    }
    printf("MPG set to %.2f\n", calc->MPG);
}

void calculateTotalCost(GasCalculator *calc) {
    // Check if required values are set (avoid division by zero)
    if (calc->MPG <= 0 || calc->currentMileage < 0 || calc->pricePerGallon < 0) {
        printf("Error: Please enter valid mileage, price per gallon, and positive MPG first!\n");
        return;
    }
    calc->totalCost = (calc->currentMileage / calc->MPG) * calc->pricePerGallon;
}

void displayResults(GasCalculator *calc) {
    clearScreen();
    printf("=== Gas Cost Calculator Results ===\n");
    printf("Current Mileage: %.2f miles\n", calc->currentMileage);
    printf("Price Per Gallon: $%.2f\n", calc->pricePerGallon);
    printf("MPG: %.2f\n", calc->MPG);
    // Only show total cost if it's been calculated (or values are valid)
    if (calc->MPG > 0 && calc->currentMileage >= 0 && calc->pricePerGallon >= 0) {
        printf("Total Gas Cost: $%.2f\n", calc->totalCost);
    } else {
        printf("Total Gas Cost: Not calculated (missing valid inputs)\n");
    }
    printf("==================================\n");
}

void clearScreen() {
    #ifdef _WIN32
        system("cls");
    #else
        system("clear");
    #endif
}

void pauseProgram() {
    printf("\nPress any key to continue...");
    while (getchar() != '\n'); // Clear buffer
    getchar(); // Wait for user input
}

Key Explanations #

1. Struct Usage: The GasCalculator struct groups all related data together, so we can pass a single pointer to functions instead of multiple individual variables. This keeps the code organized and avoids globals.
2. Menu Loop: The do-while loop in main() keeps the menu running until the user chooses to exit.
3. Input Validation: Each input function checks for valid numbers (non-negative for mileage/price, positive for MPG) and clears invalid input from the buffer to prevent infinite loops.
4. Modular Functions: Each function handles one specific task (input, calculation, display), making the code easier to read and modify.
5. Cross-Platform Support: The clearScreen() function works on both Windows and Unix-like systems.

This version is much more maintainable, follows best practices for C programming, and fits perfectly as a course assignment!

内容的提问来源于stack exchange，提问作者JustAHitman