Calculate Area&Perimeter

#include <iostream>
#include <string>
#include <cmath>

using namespace std;

bool isNumeric(string strChoose, bool isDouble)
{
    for (int i = 0; i < strChoose.length(); i++) {

        if (!isdigit(strChoose[i]) && isDouble && strChoose[i] == '.')
        {
            if (strChoose[i + 1] < '0' || strChoose[i + 1] > '9') { return false; }

        }
        else if (!isdigit(strChoose[i])) {
            return false;
        }


    }

    return true;
}

void calculateTriangle()
{
    string strInput;
    double sideA, sideB, sideC, halfP;

    cout << "Calculate perimeter and area of TRIANGLE" << endl;
    cout << "" << endl;

    do
    {
        cout << "Enter value of side A(base) in cm: ";
        cin >> strInput;


        isNumeric(strInput, true) ? sideA = stod(strInput) : sideA = 0;

    } while (sideA <= 0);

    cout << "" << endl;

    do
    {
        cout << "Enter value of side B(left hit) in cm: ";
        cin >> strInput;


        isNumeric(strInput, true) ? sideB = stod(strInput) : sideB = 0;

    } while (sideB <= 0);

    cout << "" << endl;

    do
    {
        cout << "Enter value of side C(right hit) in cm: ";
        cin >> strInput;


        isNumeric(strInput, true) ? sideC = stod(strInput) : sideC = 0;

    } while (sideC <= 0);

    cout << "" << endl;


    halfP = (sideA + sideB + sideC) / 2;

    cout << "Perimeter is: " << sideA + sideB + sideC << " cm" << endl;
    cout << "Area is: " << sqrt(halfP * (halfP - sideA) * (halfP - sideB) * (halfP - sideC)) << " cm2" << endl;
}

void calculateTrapezoid()
{
    string strInput;
    double sideA, sideB, sideC, sideD, heigth;

    cout << "Calculate perimeter and area of TRAPEZOID" << endl;
    cout << "" << endl;

    do
    {
        cout << "Enter value of side A(big base) in cm: ";
        cin >> strInput;


        isNumeric(strInput, true) ? sideA = stod(strInput) : sideA = 0;

    } while (sideA <= 0);

    cout << "" << endl;

    do
    {
        cout << "Enter value of side B(small base) in cm: ";
        cin >> strInput;


        isNumeric(strInput, true) ? sideB = stod(strInput) : sideB = 0;

    } while (sideB <= 0);

    cout << "" << endl;

    do
    {
        cout << "Enter value of side C(left hit) in cm: ";
        cin >> strInput;


        isNumeric(strInput, true) ? sideC = stod(strInput) : sideC = 0;

    } while (sideC <= 0);

    cout << "" << endl;

    do
    {
        cout << "Enter value of side D(right hit) in cm: ";
        cin >> strInput;


        isNumeric(strInput, true) ? sideD = stod(strInput) : sideD = 0;

    } while (sideD <= 0);

    cout << "" << endl;

    do
    {
        cout << "Enter value of heigth in cm: ";
        cin >> strInput;


        isNumeric(strInput, true) ? heigth = stod(strInput) : heigth = 0;

    } while (heigth <= 0);

    cout << "" << endl;

    cout << "" << endl;
    cout << "Perimeter is: " << sideA + sideB + sideC + sideD << " cm" << endl;
    cout << "Area is: " << ((sideA + sideB) * heigth) / 2 << " cm2" << endl;
}

int main()
{
    string strChoose;
    unsigned int choose;

    do
    {
        cout << "Enter value of figure\n[1]Triangle\n[2]Trapezoid\n: ";
        cin >> strChoose;
        cout << "" << endl;


        isNumeric(strChoose, false) ? choose = stoul(strChoose) : choose = 0;

        if (choose == 1) {
            calculateTriangle();

        }
        else if (choose == 2) {
            calculateTrapezoid();
        }

        if (choose >= 1 && choose <= 2) {

            cout << "" << endl;
            do
            {
                cout << "New calculation? [y/Y - Yes or n/N - No]: ";
                cin >> strChoose;

                if (strChoose == "Y" || strChoose == "y" || strChoose == "N" || strChoose == "n") {
                    break;
                }
                else {
                    strChoose == "countine";
                    continue;
                }

            } while (true);


            if (strChoose == "Y" || strChoose == "y") {
                system("CLS");
                choose = 0;
            }
            else {
                exit(0);
            }

        }


    } while (choose < 1 || choose > 2);

    return 0;
}