C程序开关不能正常工作

Question

我已经用C编写了一个程序，它使用switch语句计算并显示上周售出的产品1至5的总零售价值。如果用户输入1到5以外的数字，系统会提示他们：“不存在此类产品，请输入有效的产品编号。”但是，如果他们输入两位数字（如77），则会显示此提示两次。如果他们输入一个两位数字如36，则显示一次。下面是代码：

#include "stdafx.h" 
#include <stdio.h> 
#include <iostream> 
#include <math.h> 

unsigned int switchfn(); // prototype function for the switch statement 

    // initialize global variables 
    unsigned int productOne = 0; 
    unsigned int productTwo = 0; 
    unsigned int productThree = 0; 
    unsigned int productFour = 0; 
    unsigned int productFive = 0; 

// program execution 
int main(void) 
{ 
    // retail price of each product 
    double product1 = 2.98; 
    double product2 = 4.50; 
    double product3 = 9.98; 
    double product4 = 4.49; 
    double product5 = 6.87; 

    // user enters data for each product on each day 
    puts("Enter the product number"); 
    puts("Enter the quantity sold for Monday"); 
    unsigned int monday = switchfn(); 
    puts("Enter the the product number and quantity sold for Tuesday:"); 
    unsigned int tuesday = switchfn(); 
    puts("Enter the the product number and quantity sold for Wednesday:"); 
    unsigned int wednesday = switchfn(); 
    puts("Enter the the product number and quantity sold for Thursday:"); 
    unsigned int thursday = switchfn(); 
    puts("Enter the the product number and quantity sold for Friday:"); 
    unsigned int friday = switchfn(); 
    puts("Enter the the product number and quantity sold for Saturday:"); 
    unsigned int saturday = switchfn(); 
    puts("Enter the the product number and quantity sold for Sunday:"); 
    unsigned int sunday = switchfn(); 

    // display total amount of each product sold last week 
    puts("\nThe total amount of each product sold is:"); 
    printf("Product 1: %u\n", productOne); 
    printf("Product 2: %u\n", productTwo); 
    printf("Product 3: %u\n", productThree); 
    printf("Product 4: %u\n", productFour); 
    printf("Product 5: %u\n\n", productFive); 

    // display total retail cost for each product sold 
    puts("\nThe total dollar amount for each product sold is:"); 
    printf("Product 1: %.2f\n", productOne * product1); 
    printf("Product 2: %.2f\n", productTwo * product2); 
    printf("Product 3: %.2f\n", productThree * product3); 
    printf("Product 4: %.2f\n", productFour * product4); 
    printf("Product 5: %.2f\n\n", productFive * product5); 

    system("pause"); 
    return 0; 
} // end of program 

// switch function 
unsigned int switchfn() 
    { 
    int productNumber; // product 1 through 5 

    // only while product 1 through 5 is being entered. 
    while ((productNumber = getchar()) != EOF) { 

     switch (productNumber) { 

     case '1': 
      ++productOne; 
      break; 

     case '2': 
      ++productTwo; 
      break; 

     case '3': 
      ++productThree; 
      break; 

     case '4': 
      ++productFour; 
      break; 

     case '5': 
      ++productFive; 
      break; 

     case '\n': 
     case '\t': 
     case ' ': 
      break; 

     default: 
      printf("%s", "No such product exists."); 
      puts(" Please enter a valid product number."); 
      break; 
     } 
    } 
    return 0; 
    } 

这会涉及知道一个两位数，以及用于这种方式的任何数量大于9是一个单数而不是把每个数字作为输入？如果是这样，我将如何实现这一点？任何帮助是极大的赞赏！

Answer 1

您正在使用getch（）来读取键盘输入，该键盘输入一次只能读取一个按键。当你输入77时，它被处理为7,7。这两个都是无效的条目，所以你看到你的消息两次。输入3，6时，只有6是无效的条目，因此只显示一条消息。

如果您想要将多个字符作为单个条目进行处理，您需要更改读取方式，或许使用readln（）或其他方法。

Answer 2

而不是一次读取一个char，简单地读取行。在继续到switch()之前，代码可以对用户输入进行各种错误检查。

char buf[80]; 
if (fgets(buf, sizeof buf, stdin)) return 0; // Or something else to show EOF 
int productNumber = atoi(buf); // or strtol(), sscanf() 

switch (productNumber) { 
    // case '1': // Use numbers 
    case 1: 
     ++productOne; 
     break; 
    case 2: 
     ++productTwo; 
     break; 

    // case '\n': 
    // case '\t': 
    // case ' ':