Question

C语言Scanf()死循环问题。

输入字母或者不是数字的话 他就死循环了 怎么解决呢？
如果输入字母，如何返回到重新输入的地方。

#include <stdio.h>

#include <math.h>
int main()
{
int x,a,b,c,p;
char ch;
p=1;
do{
printf("\n请输入一个三位数:");
scanf("%d",&x);
if(x>=100 && x<=999)
{
a=x/100;
b=x/10%10;
c=x%10;
// printf("%d %d %d\n",a,b,c);
if(x==pow(a,3)+pow(b,3)+pow(c,3))
printf("\n是水仙花数!\n");
else
printf("\n不是水仙花数!\n");
printf("\n是否继续？(Y/N)\n");
scanf("%c",&ch);
scanf("%c",&ch);
if(ch=='y'||ch=='Y')
p=1;
else
p=0;
}
else
printf("\n请输入正确的三位数!\n");

// printf("%d P:",p);
// scanf("%d",&x);

}

while(p!=0);
}

Answer 1

把scanf()换成下面例子中的函数试试：

#include <stdio.h>
#include <stdlib.h>
#define    HEAD_N   10  //Input_uint(FILE *fp)函数中限制输入的最大整数位数
int Input_uint1(); //无符号整形输入函数
int Input_uint2(int digit);//无符号整形输入函数截取前digit位
int main()
{
  int a,b;
  printf("请输入赋值给变量a的整数：");
a=Input_uint1();
  printf("请输入赋值给变量b的整数（截取前3位）：");
b=Input_uint2(3);
  printf("a=%d;b=%d\n",a,b);
return 0;
}
int Input_uint1() 
{
     int count_a=0,ratio=1,count_c=0,number=0,judge=1;
     //count_a计数变量；ratio转换系数，1，10，100等；
     // count_c计数变量；number函数返回值；
     // judge输入判断变量，-1出错;
char str[HEAD_N];
    
for (count_a=0;count_a<HEAD_N;count_a++)
str[count_a]='0';
     do
{
    if (judge==1) ;
      else
{
            printf("\n输入错误。请输入一个大于等于零的整数:"); 
}
         judge=1;
 
         for(count_a=HEAD_N-1,count_c=HEAD_N-1;count_a>=0;count_a--,count_c--)
{
             str[count_a]=getchar();
             if(!((str[count_a]>='0' && str[count_a]<='9') || (str[count_a]==10)))
          judge=-1;
             if(str[count_a]==10 || count_a==0)
{  
           if(str[count_a]==10)
break;
   if(str[count_a]!=10 && count_a==0)
{   
       for(;;)
{
                        count_a=getchar();
           if(!((count_a>='0'&& count_a<='9') || (count_a==10)))
                    judge=-1;
           if (count_a==10)
              break;
}
}
            count_a=0;
}
}
         if (judge>0)
{
              for(count_a=count_c+1;count_a<HEAD_N;count_a++)
 {   
             if (str[count_a]>='0' && str[count_a]<='9')
 {
         number+=(str[count_a]-'0')*ratio;
                      ratio*=10;
 }
                  else
                 break;
 }
}
}while(judge<0);
     return number;
}
int Input_uint2(int digit) 
{
     int count_a=0,ratio=1,count_c=0,number=0,judge=1;
     //count_a计数变量；ratio转换系数，1，10，100等；
     // count_c计数变量；number函数返回值；
     // judge输入判断变量，-1出错;
char str[HEAD_N];
if (digit>HEAD_N)
digit=HEAD_N;
    
for (count_a=0;count_a<digit;count_a++)
str[count_a]='0';
     do
{
    if (judge==1) ;
      else
{
            printf("\n输入错误。请输入一个大于等于零的整数:"); 
  } 
         judge=1;
 
         for(count_a=digit-1,count_c=digit-1;count_a>=0;count_a--,count_c--)
{
             str[count_a]=getchar();
             if(!((str[count_a]>='0' && str[count_a]<='9') || (str[count_a]==10)))
          judge=-1;
             if(str[count_a]==10 || count_a==0)
{  
           if(str[count_a]==10)
break;
   if(str[count_a]!=10 && count_a==0)
{   
       for(;;)
{
                        count_a=getchar();
           if(!((count_a>='0'&& count_a<='9') || (count_a==10)))
                    judge=-1;
           if (count_a==10)
              break;
}
}
            count_a=0;
}
}
         if (judge>0)
{
              for(count_a=count_c+1;count_a<digit;count_a++)
 {   
             if (str[count_a]>='0' && str[count_a]<='9')
 {
         number+=(str[count_a]-'0')*ratio;
                      ratio*=10;
 }
                  else
                 break;
 }
}
}while(judge<0);
     return number;
}

Answer 2

问题出在scanf("%d",&x);它会读入上面输入残留的信息。
你可以用fflush(stdin);清除残余后再读

Answer 3

判断输入的是否为数字，不是数字忽略，if(isalpha(x)){continue;}

Answer 4

if(x>=100 && x<=999)改成if（(x>=100) &&( x<=999))试试