Why is the code breaking?

[VeganCheese1]

I am trying to combine my code and my group partner's code to turn in, but when I type anything that's not a integer it breaks. I think this code is what breaks it:

	cout << "Press <enter> to continue ";
	cin.ignore();
	cin.get();
	system("cls");

Can someone help me understand why this causes the code to break? Here is the full code:

#include <iostream>
using namespace std;

int main() {
	int grade_score;
	
	cout << "*****************************************\n" << "Letter Grade Converter" << endl << endl;
	cout << "Enter numerical grade (0-100 as Interger Value): ";	
	
	/* Determines if the user input is valid 
	   a then calculates the letter grade    */
	if (cin >> grade_score) {
		if (grade_score < 0) {
			cout << "Numerical grade can't be negative.";
		}
		else if (grade_score > 100) {
			cout << "Numerical grade is too large.";
		}
		
		else if (grade_score >= 90) {
			cout << "Letter grade: A";
		}	  
		else if (grade_score >= 80) {
			cout << "Letter grade: B";
		}
		else if (grade_score >= 70) {
			cout << "Letter grade: C";
		}
		else if (grade_score >= 60) {
			cout << "Letter grade: D";
		}
		else {
			cout << "Letter grade: F";
		}
	}
	else {
		cout << "Invalid Entry.";
	}
	
	cout << "\n*****************************************\n";

	//Allow the user to continue, clear the cin buffer, capture the next keystroke and clear the screen
	cout << "Press <enter> to continue ";
	cin.ignore();
	cin.get();
	system("cls");
	
	//assign input variables for month and year
	int month;
	int year;

	//assign and itialize boolean to test user input for month and year
	bool validation = false;

	//assign empty text string to hold month value
	string month_name = "";

	//assign and itialize boolean to false to check for leap year
	bool leap_year = false;

	//assign variable to hold the number of days, initialize to 0
	int days = 0;

	while (!validation) {
		//create program header
		cout << "*****************************************\nMonth Selector" << endl;

		//get input from user for month and year
		cout << "Enter year (> 0): ";
		cin >> year;
		cout << "Enter month (1 - 12): ";
		cin >> month;

		//check user input to make sure both month and year entries are valid
		if (year < 0 || month <= 0 || month > 12) {
			cout << "Enter a valid year and month" << endl;
		}
		else {
			validation = true;
		}

	}

	//check for possible leap year using user's input year
	if (year % 4 == 0 and (year % 400 == 0 or year % 100 != 0)) {
		leap_year = true;
	}

	//assign the month entered by the user to a proper month name
	switch (month) {
	case 1:
		month_name = "January";
		days = 31;
		break;
	case 2:
		month_name = "February";
		if (leap_year) {
			days = 29;
		}
		else {
			days = 28;
		}
		break;
	case 3:
		month_name = "March";
		days = 31;
		break;
	case 4:
		month_name = "April";
		days = 30;
		break;
	case 5:
		month_name = "May";
		days = 31;
		break;
	case 6:
		month_name = "June";
		days = 30;
		break;
	case 7:
		month_name = "July";
		days = 31;
		break;
	case 8:
		month_name = "August";
		days = 31;
		break;
	case 9:
		month_name = "September";
		days = 30;
		break;
	case 10:
		month_name = "October";
		days = 31;
		break;
	case 11:
		month_name = "November";
		days = 30;
		break;
	case 12:
		month_name = "December";
		days = 31;
		break;
	}

	cout << "Month name: " << month_name << endl;
	cout << "Days in Month: " << days << 
		endl << "*****************************************";
		
	return 0;
}

[seeplus]

cin.ignore() will wait for input if there's nothing to ignore. Also the stream has to be in a good state. If L37 is executed then the input stream is in a fail state. In which case the stream has to put into a good state by .clear().

Try this:

if (cin >> grade_score) {
	cin.ignore();
	if (grade_score < 0) {
		cout << "Numerical grade can't be negative.";
	} else if (grade_score > 100) {
		cout << "Numerical grade is too large.";
	}

	else if (grade_score >= 90) {
		cout << "Letter grade: A";
	} else if (grade_score >= 80) {
		cout << "Letter grade: B";
	} else if (grade_score >= 70) {
		cout << "Letter grade: C";
	} else if (grade_score >= 60) {
		cout << "Letter grade: D";
	} else {
		cout << "Letter grade: F";
	}
} else {
	cout << "Invalid Entry.";
}

cout << "\n*****************************************\n";

//Allow the user to continue, clear the cin buffer, capture the next keystroke and clear the screen
cout << "Press <enter> to continue ";
//cin.ignore();
cin.clear();
cin.get();