万能的吧友，这是哪里错了

然后通过处理字符串来判断运算

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#include<stdio.h>
#include"conio.h"
int main(void) {
double number1 = 0;
double number2 = 0;
char operation = 0;
char buff[100];
gets(buff);
sscanf(buff,"%lf%c%lf", &number1, &operation, &number2);
switch (operation) {
case '+':
printf("=%lf\n", number1 + number2);
break;
case '-':
printf("=%lf\n", number1 - number2);
break;
case '*':
printf("=%lf\n", number1 * number2);
break;
case '/':
if (number2 != 0)
printf("=%lf\n", number1 / number2);
else
printf("无效!");
break;
case '%':
if ((long)number2 != 0)
printf("=%ld\n", (long)number1 % (long)number2);
else
printf("无效！");
break;
default:
printf("输入错误！");
break;
}
return 0;
}