Input only numbers, using getch()

LabLask001.cpp

/*
 * Name: Syed Owais Ali Chishti
 * Roll No: P14-6011
 * Major: BS(CS)
 * Course: Computer Programming Lab
 * Task: 001
 */

#include<iostream>
#include<conio.h> // _getch()
#include<string>
#include<math.h>
using namespace std;

/*
 * Prototype Function
 */
void cinNumeric(double &num);

/*
 * Main
 */
void main() {
	double num[3] = {0};
	double choice;
	
	for (int i = 0; i < 3 ; i++){
		string kbData = "";
		cout << "Input " << i+1 << " number: ";
		cinNumeric(num[i]);
        cout << endl;
	}
    
    cout << endl;
	cout << "Select any option" << endl;
	cout << "1: Sum" << endl;
	cout << "2: Average" << endl;
	cout << "3: Multiply" << endl;
	cout << "Choice: ";
	cinNumeric(choice);
    cout << endl;
	if (choice == 1) {
		double sum = num[0] + num[1] + num[2];
		cout << "Sum = " << num[0] << " + " << num[1] << " + " << num[2] << " = " << sum; 
	}
	else if (choice == 2) {
		double average = (num[0] + num[1] + num[2]) / 3;
		cout << "Average = (" << num[0] << " + " << num[1] << " + " << num[2] << ") / 3 = " << average; 
	}
	else if (choice == 3) {
		double product = num[0] * num[1] * num[2];
		cout << "Multiplication = " << num[0] << " x " << num[1] << " x " << num[2] << " = " << product; 
	}
	else {
		cout << "Invalid Choice, Terminating.";
	}
	cout << endl;
}

/*
 * Return only numeric to reference variable.
 */
void cinNumeric(double &num){
    string kbData = "";
    char ch;
    while (kbData.empty()) {
        //Continue if contain value;
        while (int( ch = _getch()) != 13) {
            //Catching only integers between 0(48) - 9(57) and 46 for point (.)
            if (ch >= 48 && ch <= 57 || ch == 46)
			{
				kbData += ch;
				cout << ch;
			}
			if (ch == 8) {
				kbData.erase(kbData.end()-1,kbData.end());
				cout << "\b \b";
			}
		}


	}
	//convert string to double. Function from std library
	num = atof(kbData.c_str());
}