HARD CODE OF INTEGRATION...SOURCE CODE

/*INTEGRATION.CPP*/
#include "calculator.h"
#include <iostream>
using namespace std;
#include <math.h>
double integral(double(*f)(double x), double a, double b, int n)
{
    double step = (b - a) / n;  // width of each small rectangle
    double area = 0.0;  // signed area
    for (int i = 0; i < n; i ++)
 {
        area += f(a + (i + 0.5) * step) * step; // sum up each small rectangle
    }
    return area;
}
void ScientificCalculator::integration()
{
 cout.precision(7);
    cout<<integral(cos, 0, 3.142 / 2, 10);
}