输入y时，循环将跳过宏while循环

Question

I need help regarding this... the problem in my c is when I execute this program and when I want to repeat the roll, the roll will not be displayed from 2nd time onwards... what do I do? I dont know what to do to fix this.. got stuck here

#include <stdio.h>
#include <stdlib.h>
int main()
{
  int i, a, n, z;
  char player[5][150], b, c;
  float ave, total, f1, f2, f3;

  total = 0;
  ave = 0;
  printf("\nPlease enter number of players : ");
  scanf("%d", &a);

  for (i = 0; i < a; i++)
  {
    printf("\nEnter player %d's name : ", i + 1);
    scanf("%s", &player[i][150]);
  }

  printf("\nChoose the amount of dice used : ");
  scanf(" %d", &n);

  do
  {
    for (z = 1; z <= a; z++)
    {
      printf("\n\t%s\n ", player[z]);

      if (n == 1)
      {
        do
        {
          f1 = 1.0 + 6.0 * ((float) rand() / RAND_MAX);
          printf("\nRoll : %.0f\n", f1);
          total = f1;
          printf("Total : %.0f\n", total);
        }while (f1 == 6);
      }
      else if (n == 2)
      {
        do
        {
          f1 = 1 + (rand() % 6);
          f2 = 1 + (rand() % 6);
          printf("\nRoll : %.0f,%.0f\n", f1, f2);
          total = f1 + f2;
          printf("Total : %.0f\n", total);
        }while (f1 == f2);
      }
      else if (n == 3)
      {
        do
        {
          f1 = 1 + (rand() % 6);
          f2 = 1 + (rand() % 6);
          f3 = 1 + (rand() % 6);
          printf("\nRoll : %.0f,%.0f,%.0f\n", f1, f2, f3);
          total = f1 + f2 + f3;
          printf("Total : %.0f\n", total);
        }while (f1 == f2 && f2 == f3);
      }
    }
    printf("\nRoll again ? (y/n) = ");
    scanf("%s", &b);
  }while (b == 'y');
  printf("\n");

  ave = total / n;
  printf("Average : %.2f\n\n", ave);

  return 0;
}

Answer 1

First thing is

scanf("%s", &b);

should be

scanf("%c", &b);

And you have to flush your stdin for your do while to work.

while ((c = getchar()) != '\n' && c != EOF);

The portable way to flush stdin

Answer 2

%s reads a C string, that is a null terminated char array. The shortest string containing 'y' is a 2 character array: "y" or { 'y', '\\0'} .

So you should change char b; with char b[2]; , and use it that way:

    scanf("%1s", b);
}while (*b == 'y');

You current code writes (at least) a null after character b invoking undefined behaviour: anything can happen after that. But scanf("%1s", b); only reads first non blank character in b[0] and puts a null in b[1] : correct.

But IMHO, never mix input ignoring blank (space, tab, end of line) ( %d%s%f... ) with input explicitely processing them ( %c , fgets ), unless you are sure why you do it. So I will not advise you to use scanf("%c", b);

Answer 3

regarding this line:

scanf("%s", &b);

variable 'b' is a character, so it must be read as a character.

scanf(" %c", &b );  

note: leading space in format string so leading white space will be skipped over