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void frac_input(int &num1, int &den1, int &num2, int &den2, char &oper){
	char trash;
	bool valid;
	do{
        valid = true;
		cout << "Enter like this: 4 / 2 + 3 / 3: ";
		cin >>num1>>trash>>den1>>oper>>num2>>trash>>den2;
		if(den1 == 0 || den2 == 0){
			valid = false;
			cout << "Denominator is zero.  please retry." << endl;
		}
		if(!(isdigit(char(num1+48)) && isdigit(char(num2+48)) && isdigit(char(den1 + 48)) && isdigit(char(den2 + 48)))){
			valid = false;
			cout << "Please enter only numbers." << endl;
		}
		if(oper != '*' && oper != '/' && oper != '+' && oper != '-'){
			valid = false;
			cout << "Invalid operator.  please retry. " << endl;
		}
	} while (valid == false);
}