C++ template help, using a template for integrations

Hi i'm following a tutorial and video i found online , im trying to make a template to preform a numerical integration of a function where a user can decide which form of integration to preform, im trying to keep it to one file as not to use headers and not use massive ammounts of loops , the code for the first integration works fine on its own but when i run it through a template i get the wrong answer and the same value 1.9147e-307 for every input what am i doing wrong?

#include <iostream>
#include <cmath>
#include <ctime>
#include <cstdlib>
#include<conio.h>

using namespace std;

//declared function
double F(double X)
{
   double f;

   f = (X*X);
   return f;
};

double unifRand()
{
    return rand() / double(RAND_MAX);
};

template<typename T> class INTG{
    private:
        T a;
        T b;
        T n;
    public:
        INTG(T a, T b,T n){
            INTG::a = a;
            INTG::b = b;
        }

        ~INTG(){}

        T MC() {
            // some code

            return ans;}

        T SIMPC(){ // Simpson integration code here
            re开发者_开发问答turn a+b+n;
        }
};

int main() {
    double a,b,mc,simp,ans;
    int OP,n;
    cout<<"Enter 1 for Monte Carlo Integration , Enter 2 for Composite Simpson Integration, enter 3 for trapezoidal int...."<<endl;
    cin>>OP;
    clock_t start = clock();


    if (OP == 1) {
        cout<<"Enter lower limit of integration"<<endl;
        cin>>a;
        cout<<"Enter upper limit of integration"<<endl;
        cin>>b;
        cout<<"Enter number of iterations"<<endl;
        cin>>n;
        ans = INTG<double>::MC(a, b, n);
        INTG<double> MyCalc(a,b,n);

        cout<< ans <<endl;

        //mc =  INTG::MC(a, b, n);
        getch();
    }
}

---

ans is never assigned a value. That would account for your 1.9147e-307.

Did you intend

ans = MyCalc.MC();

before the cout ?

Also

INTG(T a, T b,T n){
    INTG::a = a;
    INTG::b = b;
}

Is better described as

INTG(T a, T b, T n):a(a),b(b),n(n) {}

Initializing instead of assigning, and remembering n.

So the calculation sequence would be

INTG<double> MyCalc(a,b,n);
ans = MyCalc.MC();

---

if (OP = 1) {

...should be...

if (OP == 1) {