C++ 아주 간단한 문제인데요..

#include <iostream>
#include <fstream>
 
using namespace std;
 
void Calc(int firstNum, int lastNum, char operatorKind, double &rresult)
{
	if(operatorKind == '+') rresult = firstNum + lastNum;
	else if(operatorKind == '-') rresult = firstNum - lastNum;
	else if(operatorKind == '*') rresult = firstNum * lastNum;
	else if(operatorKind == '/') rresult = firstNum / lastNum; // 왜 소수점이 안뜨지
	else if(operatorKind == '%') rresult = firstNum % lastNum;
	else rresult = false;
}
 
void main(void)
{
	int    count;
	int    firstNum;
	int    lastNum;
	char   operatorKind;
	double result;
 
	ifstream fin("input.txt");
	ofstream fout("output.txt");
 
	fin >> count;
 
	for(int i = 1; i <= count; i++) {
		fin >> firstNum >> operatorKind >> lastNum;
		Calc(firstNum, lastNum, operatorKind, result);
 
		if(result == false) {
			fout << firstNum << " " << operatorKind << " " << lastNum << " = " << "유효하지 않은 연산자" << endl;
			cout << firstNum << " " << operatorKind << " " << lastNum << " = " << "유효하지 않은 연산자" << endl;
		} else {
			fout << firstNum << " " << operatorKind << " " << lastNum << " = " << result << endl;
			cout << firstNum << " " << operatorKind << " " << lastNum << " = " << result << endl;
		}
 
	}
}