please help...when case 2, 3, or 4 are chosen the program goes into an infinite loop except for case 1 which works fine....

//this program performs addition (grades 1,2,3,4), subtraction (grades 2,3,4), multiplication (grades 3,4), and division(grade 4)

#include <cstdlib> 
#include <ctime> 
#include <iostream> 

using namespace std; 

int main() 
{ 
	srand((unsigned)time(0)); 

	int grade, operation2, operation3, operation4;
	int random_integer1, random_integer2; 
	int userans, compans;
	char ans;

	do
	{
		cout << "If you are in 1st Grade, type '1'" << endl;
		cout << "If you are in 2nd Grade, type '2'" << endl;
		cout << "If you are in 3rd Grade, type '3'" << endl;
		cout << "If you are in 4th Grade, type '4'" << endl;
		cout << "Type '5' if you don't feel like having fun with ";
		cout << "numbers right now :-D" << endl;
		cout << "Type in your choice here--> ";
		cin >> grade;
		cout << endl;

		switch (grade)
		{
		case 1:
			do
			{
			for(int index=0; index<20; index++)
			random_integer1 = (rand()%10)+1; 
			random_integer2 = (rand()%10)+1; 
			compans = random_integer1 + random_integer2;

			cout << random_integer1 << " + " << random_integer2 << " = ";
			cin >> userans;

			if (userans == compans)
				cout << "That's correct! Good job!\n";
			else
				cout << "Good try, but the correct answer is " << compans << endl;

			cout << "Do you want to try another one?\n";
			cout << "Type y for yes, and n for no: ";
			cin >> ans;
			cout << endl;
			}
			while (ans =='y' || ans == 'Y');

		cout << "That was awesome! :-D\n";

		break;

	case 2:
		
			cout << "Type A for addition or type S for subtraction: ";
			cin >> operation2;
			
			switch (operation2)
			{
			case 'A':
			case 'a':
			do
			{
			for(int index=0; index<20; index++)
			random_integer1 = (rand()%100)+1; 
			random_integer2 = (rand()%100)+1; 
			compans = random_integer1 + random_integer2;

			cout << random_integer1 << " + " << random_integer2 << " = ";
			cin >> userans;

			if (userans == compans)
				cout << "That's correct! Good job!\n";
			else
				cout << "Good try, but the correct answer is " << compans << endl;

			cout << "Do you want to try another one?\n";
			cout << "Type y for yes, and n for no: ";
			cin >> ans;
			cout << endl;
			}
			while (ans =='y' || ans == 'Y');

		cout << "That was awesome! :-D\n";
		break;

			case 'S':
			case 's':
			do
			{
			for(int index=0; index<20; index++)
			random_integer1 = (rand()%100)+1; 
			random_integer2 = (rand()%100)+1; 
			compans = random_integer1 - random_integer2;

			cout << random_integer1 << " - " << random_integer2 << " = ";
			cin >> userans;

			if (userans == compans)
				cout << "That's correct! Good job!\n";
			else
				cout << "Good try, but the correct answer is " << compans << endl;

			cout << "Do you want to try another one?\n";
			cout << "Type y for yes, and n for no: ";
			cin >> ans;
			cout << endl;
			}
			while (ans =='y' || ans == 'Y');

		cout << "That was awesome! :-D\n";
		break;

		default:
		cout << "That choice is not acceptable.";
			}


	case 3:
			cout << "Type A for addition, S for subtraction, M for multiplication: ";
			cin >> operation3;
			
			switch (operation3)
			{
			case 'A':
			case 'a':
			do
			{
			for(int index=0; index<20; index++)
			random_integer1 = (rand()%1000)+1; 
			random_integer2 = (rand()%1000)+1; 
			compans = random_integer1 + random_integer2;

			cout << random_integer1 << " + " << random_integer2 << " = ";
			cin >> userans;

			if (userans == compans)
				cout << "That's correct! Good job!\n";
			else
				cout << "Good try, but the correct answer is " << compans << endl;

			cout << "Do you want to try another one?\n";
			cout << "Type y for yes, and n for no: ";
			cin >> ans;
			cout << endl;
			}
			while (ans =='y' || ans == 'Y');

		cout << "That was awesome! :-D\n";
		break;

			case 'S':
			case 's':
			do
			{
			for(int index=0; index<20; index++)
			random_integer1 = (rand()%1000)+1; 
			random_integer2 = (rand()%1000)+1; 
			compans = random_integer1 - random_integer2;

			cout << random_integer1 << " - " << random_integer2 << " = ";
			cin >> userans;

			if (userans == compans)
				cout << "That's correct! Good job!\n";
			else
				cout << "Good try, but the correct answer is " << compans << endl;

			cout << "Do you want to try another one?\n";
			cout << "Type y for yes, and n for no: ";
			cin >> ans;
			cout << endl;
			}
			while (ans =='y' || ans == 'Y');

		cout << "That was awesome! :-D\n";
		break;

			case 'M':
			case 'm':
			do
			{
			for(int index=0; index<20; index++)
			random_integer1 = (rand()%100)+1; 
			random_integer2 = (rand()%10)+1; 
			compans = random_integer1 * random_integer2;

			cout << random_integer1 << " * " << random_integer2 << " = ";
			cin >> userans;

			if (userans == compans)
				cout << "That's correct! Good job!\n";
			else
				cout << "Good try, but the correct answer is " << compans << endl;

			cout << "Do you want to try another one?\n";
			cout << "Type y for yes, and n for no: ";
			cin >> ans;
			cout << endl;
			}
			while (ans =='y' || ans == 'Y');

		cout << "That was awesome! :-D\n";
		break;

		default:
		cout << "That choice is not acceptable.";
			}




	case 4:
			cout << "Type A for addition, S for subtraction, \n";
			cout << "M for multiplication, or D for division: ";
			cin >> operation4;
			
			switch (operation4)
			{
			case 'A':
			case 'a':
			do
			{
			for(int index=0; index<20; index++)
			random_integer1 = (rand()%10000)+1; 
			random_integer2 = (rand()%10000)+1; 
			compans = random_integer1 + random_integer2;

			cout << random_integer1 << " + " << random_integer2 << " = ";
			cin >> userans;

			if (userans == compans)
				cout << "That's correct! Good job!\n";
			else
				cout << "Good try, but the correct answer is " << compans << endl;

			cout << "Do you want to try another one?\n";
			cout << "Type y for yes, and n for no: ";
			cin >> ans;
			cout << endl;
			}
			while (ans =='y' || ans == 'Y');

		cout << "That was awesome! :-D\n";
		break;

			case 'S':
			case 's':
			do
			{
			for(int index=0; index<20; index++)
			random_integer1 = (rand()%10000)+1; 
			random_integer2 = (rand()%10000)+1; 
			compans = random_integer1 - random_integer2;

			cout << random_integer1 << " - " << random_integer2 << " = ";
			cin >> userans;

			if (userans == compans)
				cout << "That's correct! Good job!\n";
			else
				cout << "Good try, but the correct answer is " << compans << endl;

			cout << "Do you want to try another one?\n";
			cout << "Type y for yes, and n for no: ";
			cin >> ans;
			cout << endl;
			}
			while (ans =='y' || ans == 'Y');

		cout << "That was awesome! :-D\n";
		break;

			case 'M':
			case 'm':
			do
			{
			for(int index=0; index<20; index++)
			random_integer1 = (rand()%100)+1; 
			random_integer2 = (rand()%100)+1; 
			compans = random_integer1 * random_integer2;

			cout << random_integer1 << " * " << random_integer2 << " = ";
			cin >> userans;

			if (userans == compans)
				cout << "That's correct! Good job!\n";
			else
				cout << "Good try, but the correct answer is " << compans << endl;

			cout << "Do you want to try another one?\n";
			cout << "Type y for yes, and n for no: ";
			cin >> ans;
			cout << endl;
			}
			while (ans =='y' || ans == 'Y');

		cout << "That was awesome! :-D\n";
		break;

			case 'D':
			case 'd':
			do
			{
			for(int index=0; index<20; index++)
			random_integer1 = (rand()%20)+1; 
			random_integer2 = (rand()%10)+1; 
			compans = random_integer1 / random_integer2;

			cout << random_integer1 << " / " << random_integer2 << " = ";
			cin >> userans;

			if (userans == compans)
				cout << "That's correct! Good job!\n";
			else
				cout << "Good try, but the correct answer is " << compans << endl;

			cout << "Do you want to try another one?\n";
			cout << "Type y for yes, and n for no: ";
			cin >> ans;
			cout << endl;
			}
			while (ans =='y' || ans == 'Y');

		cout << "That was awesome! :-D\n";
		break;

		default:
		cout << "That choice is not acceptable.";
			}


	case 5:
		cout << "Ok, we'll have fun with numbers some other time.\n";
		cout << "Good-bye for now! :-D\n";
	exit(1);

	default:
		cout<<"That value does not exist";
	}
}while (grade != 5);
	
return 0;
}

Code tags added. -Narue

cout << "Type A for addition or type S for subtraction: ";
cin >> operation2;

switch (operation2)

I'm not sure since theres way too much code, but to me i think here your trying to enter a char into an int...which could be your problem

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