程序代码：

//VC6.0下，测试
#include<stdio.h>
int strr_index(char *string, char letter){
   char *original = string;
   char *ptr = NULL;
   while(*string){
      if(*string == letter){//跟踪调试到第2次调用时在这里出错
         ptr = string;
      }
      string++;
   }
   return ((*ptr)==letter ? ptr-original: string-original);
}                          
    
void main(void){
    printf("Location of C is %d\n", strr_index("1001 C/C++", 'C'));
    printf("Location of x is %d\n", strr_index("1001 C/C++", 'x'));//不能执行这一步
    getchar();
}