Integral of x^2

#include <iostream>

using namespace std;

double f(double n){
    return n * n;
}

double maxNumber(double a, double b){
    if(a >= b)
        return a;
    else
        return b;
}

double minNumber(double a, double b){
    if(a >= b)
        return b;
    else
        return a;
}

int main()
{
    // Inputs from the user
    cout << "I will calculate the area of the function f(x) = x^2 from a to b.\n";
    cout << "Give me the a: ";
    double a;
    cin >> a;
    cout << "Give me the b: ";
    double b;
    cin >> b;
    cout << endl;
    // Determine the minNumber and the maxNumber
    double maximum = maxNumber(a, b);
    double minimum = minNumber(a, b);
    // Calculate
    double sum = 0.0;
    double step = 0.000001;                  // Step = Basis of the rectangle
    for(double i=minimum; i<=maximum; i+=step){
        sum += step * f(i);
    }

    // Display the result
    cout << "Area E = ";
    if(a <= b){
        cout << sum << endl;
    }
    else{
        cout << -sum << endl;
    }

    return 0;
}