My while statement is getting infinite loop? [closed] - c++

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#include "stdafx.h"
#include <iostream>
#include <string>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
using namespace std;
//this program will let the user input their assignment score and see their letter grade
int main() {
int score;
cout << "Input your score: ";
//to make the while loop
int x = 1;
while (x == 1) {
cin >> score;
if (score >= 90){
cout << "\nA";
break;
}
else if (score >= 80) {
cout << "\nB";
break;
}
else if (score >= 70) {
cout << "\nC";
break;
}
else if (score >= 60) {
cout << "\nD";
break;
}
else if (score >= 0) {
cout << "\nF";
break;
}
else
cout << "\nInvalid input";
}
}
I'm trying to write a program that let the user input their score for an assignment and display their resulting letter grade. If the user input is not a valid score, it prints "Invalid input" and should ask for user input again. However, when I actually run the program and type in an invalid value, it goes into an infinite loop of printing "Invalid input". Why is this? Thanks in advance.

Answer 1

When the user enters invalid input, cin >> score fails and leaves an error flag set on the stream.
Subsequent read operations just don't do anything until you clear that flag with std::basic_ios::clear().
Furthermore, since the read failed, score has some unspecified value (as you did not initialise it), and apparently on your test runs that unspecified value happens not to match any of those continues, so you never hit a break.
Instead of just:
std::cin >> score;
Try this:
if (!(cin >> score)) {
// If reading into an int failed, we come here
cout << "Invalid value! Try again" << endl;
// Clear error flag
cin.clear();
// Restart the loop
continue;
}
You may also need to ask the stream to eat up newlines in the input buffer. If you get the "Invalid value!" message twice, look up on SO how to do that.

Answer 2

you set x=1 and check if x==1. For the compiler it seems that it could be an infinite loop because it's unsure if a break would happen, that's why it's only a Warning and not an Error. For that behaviour you don't even need to vast the variable x , you could use while(true) too.