Integration

#include "stdafx.h"
#include <stdio.h>
#include <math.h>

double func(double x) {
    return x * x;
}

double IntegrateRect(double a, double b, double step) {
    double ans = 0.0;
    int stepRect = 0;
    for (double x = a; x < b; x += step) {
        ans += fmin(step, b - x) * func(x);
        stepRect += 1;
    }
    return ans;
}



double IntegrateTrap(double a, double b, double step) {
    double ans = 0.0;
    int stepTrap = 0;
    for (double x = a; x < b; x += step) {
        ans += fmin(step, b - x) * (func(x) + func(x + step)) / 2;
        stepTrap += 1;
    }
    //printf("%d\n", stepTrap);
    return ans;
}

double IntegrateT(double a, double b, double precision) {
    double area = (b - a) * (func(b) + func(a)) / 2;
    double areaOld = -10000000.0;
    int i = 1;
    int step = 0;
    while ((fabs(area - areaOld)) > precision) {
        step += 1;
        areaOld = area;
        i++;
        area = IntegrateTrap(a, b, (b - a) / i);
    }
    printf("%d\n", step);
    return area;

}

int main(void) {
    printf("Enter interval [a, b] and step (x)\n");

    double a, b, step;
    scanf_s("%lf %lf %lf", &a, &b, &step);
    printf("%f %f %f\n", a, b, step);
    //a = 0.0; b = 1.0; step = 0.01;

    //printf("Integrated with rectangles:");
    printf("Integrated with rectangles: %f\n", IntegrateRect(a, b, step));
    printf("Integrated with trapezoids: %f\n", IntegrateTrap(a, b, step));
    printf("Integrated with another function: %f\n", IntegrateT(a, b, step));

    scanf_s("%lf", &a);
    return 0;
}