判断花括号是否匹配

#include<stdio.h>  int main()  {      int ch;      int a;      while ((ch=getchar())!=EOF)      {          if (ch=='{')          {              a++;          }          else if(ch=='}'&&a!=0)          {              a--;          }          else if(ch=='}'&&a==0)          {              printf("unmatched\n");              return 0;          }      }      if(a==0)      {          printf("matched\n");      }      else      {          printf("unmathed\n");      }      return 0;  }