如何在C编程中的if else语句中使用循环

Question

我需要构建一种读取会员类型和项目价格的算法。 输出将是折扣后支付的金额。 该程序允许小写和大写字符输入，如果输入的代码无效，将提示用户重新进入会员类型。

会员人数如下： 铂 - p -30％ 黄金-G -20％ 银 - S- 10％ 当正确插入会员时，非会员-x -0％

I设法获得输出（P，G，S或X）。但是，当插入错误的字符时，我不确定如何重复该程序，直到获得正确的输出为止...

int main()
{
   
    
    printf("Suria Supermarket");
    
    char membershipType;
    char membershipTypeTwo;
    float itemPrice;
    
    
    char membershipType2;
    float itemPrice2;
    
    printf("\nEnter membership type (S or G or P, X for non-member): %c", membershipType);
    scanf("%c", &membershipType);
    
    printf("Enter item price (RM): ",itemPrice); 
    scanf("%f",&itemPrice);
    
    
   float discountedAmount;
   float discountedAmount2;
       
    if(membershipType=='s') {
        printf("\n");
        printf("Item Price: RM %1.2f", itemPrice);
        printf("\n");
        printf("Membership Type: %c",membershipType);
        printf("\n");
        printf("Discount (%%): 10\n");
        discountedAmount = ((itemPrice)-(itemPrice*0.1));        
        printf("Discounted Price: RM %1.2f", discountedAmount);
        
    }
    else if(membershipType=='S') {
        printf("\n");
        printf("Item Price: RM %1.2f", itemPrice);
        printf("\n");
        printf("Membership Type: %c",membershipType);
        printf("\n");
        printf("Discount (%%): 10\n");
        discountedAmount = ((itemPrice)-(itemPrice*0.1));        
        printf("Discounted Price: RM %1.2f", discountedAmount);
        
    } 
    else if(membershipType=='g') {
        printf("\n");
        printf("Item Price: RM %1.2f", itemPrice);
        printf("\n");
        printf("Membership Type: %c",membershipType);
        printf("\n");
        printf("Discount (%%): 20");
        printf("\n");
        discountedAmount = ((itemPrice)-(itemPrice*0.2));        
        printf("Discounted Price: RM %1.2f", discountedAmount);
    } 
    else if(membershipType=='G') {
        printf("\n");
        printf("Item Price: RM %1.2f", itemPrice);
        printf("\n");
        printf("Membership Type: %c",membershipType);
        printf("\n");
        printf("Discount (%%): 20");
        printf("\n");
        discountedAmount = ((itemPrice)-(itemPrice*0.2));        
        printf("Discounted Price: RM %1.2f", discountedAmount);
    } 
    else if(membershipType=='p') {
        printf("\n");
        printf("Item Price: RM %1.2f", itemPrice);
        printf("\n");
        printf("Membership Type: %c",membershipType);
        printf("\n");
        printf("Discount (%%): 30");
        printf("\n");
        discountedAmount = ((itemPrice)-(itemPrice*0.3));        
        printf("Discounted Price: RM %1.2f", discountedAmount);
    } 
    else if(membershipType=='P') {
        printf("\n");
        printf("Item Price: RM %1.2f", itemPrice);
        printf("\n");
        printf("Membership Type: %c",membershipType);
        printf("\n");
        printf("Discount (%%): 30");
        printf("\n");
        discountedAmount = ((itemPrice)-(itemPrice*0.3));        
        printf("Discounted Price: RM %1.2f", discountedAmount);
    } 
    else if(membershipType=='x'){
        printf("\n");
        printf("Item Price: RM %1.2f", itemPrice);
        printf("\n");
        printf("Membership Type: %c",membershipType);
        printf("\n");
        printf("Discount (%%): 0");
        printf("\n");      
        printf("Discounted Price: RM %1.2f", itemPrice);
    }
        else if(membershipType=='X') {
        printf("\n");
        printf("Item Price: RM %1.2f", itemPrice);
        printf("\n");
        printf("Membership Type: %c",membershipType);
        printf("\n");
        printf("Discount (%%): 0");
        printf("\n");      
        printf("Discounted Price: RM %1.2f", itemPrice);
    }
    else {
        printf("Invalid code, please enter again.");
        printf("\n");
        printf("\n");
        if(membershipTypeTwo!='s','S','g','G','p','P','x','X');
        
        printf("Enter membership type (S or G or P, X for non-member): %c",membershipTypeTwo);
        scanf("%c%*c",&membershipTypeTwo);
        printf("Enter item price (RM): ",itemPrice); 
        scanf("%f",&itemPrice);
        
            
}

       return 0;

}```

Answer 1

而不是大的if-else梯子使用switch语句

switch(toupper((unsigned char)membershipType))
{
    case 'P':
    /* ... */
    break;
    case 'G':
    /* ... */
    break;
    default:
        print("Wrong membership type\n");
    break;
}

Answer 2

编写一个循环以读取输入值，仅在输入流上有匹配或错误条件时退出。

作为劳动力减少的一点，您可以将所有有效的成员资格类型放入“ PGSX”之类的字符串中是字符串的一部分，而不是明确检查每个可能的字符。您还可以使用toupper或tolower函数将输入转换为另一种情况以进行比较。

/**
 * These headers are necessary for the code below.
 */
#include <string.h>
#include <ctype.h>
#include <stdbool.h>
...
/**
 * Create a flag to tell us if we need to keep scanning
 * for input.
 */
bool done = false;
...
while ( !done )
{
  /**
   * Stores the number of items read from scanf.
   */
  int itemsRead;

  /**
   * Create a string with the valid input characters.
   */
  const char *membershipTypeList = "PGSX";

  printf( "\nEnter membership type..." );
  /**
   * The leading blank in the " %c" format string
   * tells scanf to skip over any leading whitespace
   * so you don't accidentally pick up a newline from
   * a previous entry.
   *
   * scanf returns the number of items successfully
   * read and assigned, or EOF on end-of-file or 
   * error.  A return value of 1 means we read *something*;
   * we then compare that against the values in the 
   * membershipTypeList string.  If strchr returns
   * NULL, the the character wasn't in the string
   * and we prompt the user to try again.  A return 
   * value of 0 means we had a matching failure, 
   * which almost never happens with %c because 
   * it will match any printing character.  A
   * return value of EOF means scanf either saw
   * and end of file condition or an error on
   * the input stream.
   */
  if ( (itemsRead = scanf( " %c", &membershipType )) == 1 )
  {
    /**
     * You can assign the result of a comparison
     * to an int or boolean variable.  If this
     * looks too weird for you, you can replace 
     * it with:
     *
     *    if ( strchr(...) != NULL )
     *      done = true;
     */
    done = strchr( membershipTypeList, 
      toupper( membershipType ) ) != NULL;

    if ( !done )
       printf( "\nThat wasn't a valid membership type, try again..." );
  }
  else if ( itemsRead == 0 )
  {
    printf( "\nMatching failure on input, try again..." );
  }
  else
  {
    done = true;
  }
}
/**
 * Check to see if we exited the loop because
 * a problem with the stream
 */
if ( feof( stdin ) || ferror( stdin ) )
{
  fprintf( stderr, "Error on input stream, exiting...\n" );
  exit( -1 );
}

/**
 * Process membershipType as normal
 */

欢迎处理C中的交互式输入。通常，屁股很痛苦。