c - scanf 格式字符串需要类型参数

Question

我的代码有很多问题，并且有人尝试向我解释它，但我仍然无法理解我做错了什么......这一切在我的脑海中似乎都是正确的。据我了解，我的字符扫描不正确。我也有返回值的问题，并且我的“int * 与 int 的间接级别不同”。我该如何修复我的代码？我完全迷失了。

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

#define PAUSE system("pause")
#define CLS system("cls")
#define FLUSH flush()

// PROTOTYPE FUNCTIONS
void displayMenu();
void flush();
char getUserChoice();
int newSale(int *price, char *firstTime, char *veteran, char *student, char *lastDay);
int outputPrice(int carSales[], int *carsSold, int *avgCarPrice, int *totalRevenue);

// MAIN
main() {
    int carSales[500] = { 0 };
    int price = 0,  avgCarPrice = 0, totalRevenue = 0, carsSold = 0;
    char firstTime = 'n', veteran = 'n', student = 'n', lastDay = 'n';


    char userSelection;
    do {
        userSelection = getUserChoice();
        switch (userSelection) {
        case  'A': // ENTER A NEW SALE
            newSale(&price, &firstTime, &veteran, &student, &lastDay); // call function to ask questions
            printf("\nPRICE OF CAR: %i\n", price);
            carsSold++; // will add to +1 to the amount of cars sold
            carSales[carsSold] = price; // add the car to carSales array
            PAUSE;
            break;
        case  'B': // OUTPUT STATS
            outputPrice(&carSales[500], &carsSold, &avgCarPrice, &totalRevenue);
            PAUSE;
            break;
        case  'Q': //  Quit Program
            printf("Thanks....\n");
            break;
        default: // Invalid Selection
            printf("Invalid selection...try again!\n");
            PAUSE;
            break;
        } // end switch
    } while (userSelection != 'Q');
    PAUSE;
} // end of main

  // DISPLAY THE MENU
void displayMenu() {
    CLS;
    printf("========== MAIN MENU ==========\n");
    printf("A. ENTER NEW CAR\n");
    printf("B. OUTPUT STATS\n");
    printf("Q. QUIT\n");
    printf("Enter your choice: ");
} // end displayMenu

  // FLUSH
void flush() {
    while (getchar() != '\n');
} // end flush

  // GET THE USER CHOICE
char getUserChoice() {
    char result;
    displayMenu();
    scanf("%c", &result); FLUSH;
    result = toupper(result);
    return result;
} // end getUserChoice

int newSale(int *price, char *firstTime, char *veteran, char *student, char *lastDay) {

    // ASK QUESTIONS

    printf("What is the sticker price of the car?\n"); 
    scanf("%i", &price);

    printf("Are you a first time buyer? (y/n)\n");
    scanf("%s", firstTime);

    printf("Are you a veteran? (y/n)\n");
    scanf("%s", veteran);

    printf("Are you a student (y/n)\n");
    scanf("%s", student);

    printf("Is it the last day of the month? (y/n)\n");
    scanf("%s", lastDay);

    // CALCULATE PRICES

    if (*lastDay == 'y') { // car is discounted by 3% if user said yes
        *price = *price - (((int)(*price) * 3) / 10); // (int) is added to keep the cocmpiler from complaining due to an implicit cast to floating point. 
    }

    if (*firstTime == 'y') {  // if it's the user's first time buying, $100 is given in credit
        *price = *price - 100;
    }

    if (*student == 'y' && firstTime == 'y') { // car is discounted by $200 if user is a student and first time buyer- they also recieve the other discounts
        *price = *price - ((int)(*price) - 200);
    }

    if (*veteran == 'y') { // veterans recieve 2% off the final price of the car
        *price = *price - (((int)(*price) * 2) / 10);
    }

    return price;
}

int outputPrice(int carSales[ ], int *carsSold, int *avgCarPrice, int *totalRevenue) {
    printf("The total cars sold is: %i", carsSold); // Display the amount of cars sold

    for (int i = 0; i < 500; ++i) { // add all the prices in carSales 
        *totalRevenue = *totalRevenue + carSales[i];
    }

    printf("The Average car sold price: %i", avgCarPrice); // Display the avg price of the cars
    printf("Total revenue: %i", totalRevenue); // Display total revenue
    return;
}

Answer 1

首先，outputPrice函数的返回类型应该是void而不是int；当我最初尝试编译您的代码时，这给了我一个错误。

接下来，在 newSale 函数中，该行

scanf("%i", &price);

应改为

scanf("%i", price);

因为price已经是一个指针。在其他四个 scanf 调用中，%s 应更改为 `%c;例如

scanf("%s", firstTime);

应改为

scanf("%c", firstTime);

%s 是字符串的格式说明符； %c 用于字符。另请注意，参数仍然不需要通过在其名称前添加 & 来引用，因为它们也已经是指针。第三个 if 语句的第一行应更改为

if (*student == 'y' && firstTime == 'y') {

至

if (*student == 'y' && *firstTime == 'y') {

请注意 firstTime 前面的 &。这是必要的，因为 firstTime 是一个指针，而不是字符，因此将其与字 rune 字 'y' 进行比较将产生不正确的结果结果。但是，firstTime 是指向字符的指针，因此使用 * 取消引用它会返回一个字符，然后可以将其与字 rune 字进行比较，而不会出现问题。 return语句也有问题:

return price;

应该是

return *price;

因为函数的返回类型是int，而price是一个int指针。

在 outputPrice 函数中，所有 printf 语句中的参数都需要取消引用。例如

printf("The total cars sold is: %i", carsSold);

应该是

printf("The total cars sold is: %i", *carsSold);

因为 carsSold 是一个 int 指针，而不是 int 本身。

此外，需要为 main 指定返回类型 int 以避免编译器警告。