macOS beginner c++ prob-check if user input is numeric

[seventeen]

I am creating a simple CLI calculator tool as an exercise. The complete code is included below. I need to make sure n1 and n2 are numeric in order for the functions to work; somewhat consequently, I would like to make the program quit upon coming across a non-numeric value from the user.

Can anyone give me some direction?

Check out the first if statement in the do block. (its commented out)

Thank you!

#include <iostream>
#include <new>

using namespace std;

double factorial(double n) { return (n <= 1) ? 1 : n * factorial(n - 1); }
double add(double n1, double n2) { return(n1 + n2); }
double subtract(double n1, double n2) { return(n1 - n2); }
double multiply(double n1, double n2) { return(n1 * n2); }
double divide(double n1, double n2) { return(n1 / n2); }
int modulo(int n1, int n2) { return(n1 % n2); }
double power(double n1, double n2) {
	double n = n1;
	for(int i = 1 ; i < n2 ; i++) {
		n *= n1;
	}
	return(n);
}

void print_problem(double n1, double n2, char operatr) {
	cout<<n1<<operatr<<flush;
	if(operatr != '!') {
		cout<<n2<<flush;
	}
	cout<<"="<<flush;
}

int main(void) {
	
	double* n1, * n2, * result = NULL;
	char* operatr = NULL;
	
	n1 = new (nothrow) double;
	n2 = new (nothrow) double;
	result = new (nothrow) double;
	operatr = new (nothrow) char;
		
	if(n1 == NULL || n2 == NULL || operatr == NULL || result == NULL) {
		cerr<<"\nMemory allocation failure.\n"<<endl;
	} else {
		
		do {
			
			cout<<"calculator>> "<<flush;
			cin>>*n1;
			
			// if(*n1 is not numeric) {
			// 		 break;
			// }

			cin>>*operatr;
			
			if(*operatr == '!') {
				print_problem(*n1, *n2, *operatr);
				cout<<factorial(*n1)<<endl;
			} else {
				
				cin>>*n2;
				
				switch(*operatr) {
					case '+':
						print_problem(*n1, *n2, *operatr);
						cout<<add(*n1, *n2)<<endl;
						break;
					case '-':
						print_problem(*n1, *n2, *operatr);
						cout<<subtract(*n1, *n2)<<endl;
						break;
					case '*':
						print_problem(*n1, *n2, *operatr);
						cout<<multiply(*n1, *n2)<<endl;
						break;
					case '/':
						if(*n2 > 0) {
							print_problem(*n1, *n2, *operatr);
							cout<<divide(*n1, *n2)<<endl;
						} else {
							print_problem(*n1, *n2, *operatr);
							cout<<" cannot be computed."<<endl;
						}
						break;
					case '%':
						if(*n1 >= 0 && *n2 >= 1) {
							print_problem(*n1, *n2, *operatr);
							cout<<modulo(*n1, *n2)<<endl;
						} else {
							print_problem(*n1, *n2, *operatr);
							cout<<" cannot be computed."<<endl;
						}
						break;
					case '^':
						print_problem(*n1, *n2, *operatr);
						cout<<power(*n1, *n2)<<endl;
						break;
					default:
						cout<<"Invalid Operator"<<endl;
				}
			}
		} while(true);
		
		delete n1, n2, operatr, result;
	}
	return(0);
}

 

[Sander]

They will always be numeric, since they're doubles. You probably want to check this before assigning the user input to the variables, by reading the user input as a string and then converting it.

Also, please get rid of the news. There is absolutely no need to do this via pointers. Did you perhaps grow up on Java or C#..?