p;   }
    else{
     NumA = FTop(Operands);
     FPop(Operands);
     if (NumB == 0){
      PrintError = 1;                   /*分母不为0*/
     }
     else{
      answer = (float)(NumA / NumB);   /* x / y*/
      FPush(answer,Operands);
     }
    }
    break;
   case '+':                                      /*加法运算*/
    NumB = FTop(Operands);
    FPop(Operands);
    if (FIsEmpty(Operands)){ 
     PrintError = 1;
    }
    else{
     NumA = FTop(Operands);
     FPop(Operands);
     answer = NumA + NumB;    /* x + y*/
     FPush(answer,Operands);
    }
    break;
   case '-':                                      /*减法运算*/
    NumB = FTop(Operands);
    FPop(Operands);
    if (FIsEmpty(Operands)){ 
     PrintError = 1;
    }
    else{
     NumA = FTop(Operands);
     FPop(Operands);
     answer = NumA - NumB;    /* x - y*/
     FPush(answer,Operands);
    }
    break;
   default:
    PrintError = 1;
    break;
   }                                          /*判断结束*/
   Pop(Whereat);
  }
 }                                                  /*循环结束*/
 if (!PrintError){  
  answer =  FTop(Operands);
  FPop(Operands);
  if (FIsEmpty(Operands) != 1){
   fprintf(Change,"Error in infix notation.");         /*如果还有操作数*/
   PrintError = 0;
  }
  else
   fprintf(Change,"%.2f",answer);   
 }
 else{
  fprintf(Change,"Error in infix notation.");   
  PrintError = 0;
 }
 FMakeEmpty(Operands);
 free(Operands);
}