integral

#include <stdio.h>
#include <iostream>
float left_triangle_method();
float right_triangle_method();
float central_triangle_method();
float trapezium_method();


int main()
{
    std::cout << left_triangle_method() << "\n\n";
    std::cout << right_triangle_method() << "\n\n";
    std::cout << central_triangle_method() << "\n\n";
    std::cout << trapezium_method() << "\n\n";
    return 0;
}


float left_triangle_method()
{
    int n;
    float sum = 0;
    float a = 0.4;
    float b = 1.2;
    float h;
    float result;
    float x;

    std::cout << "Enter n for left-triangle method\n";
    std::cin >> n;

    h = (b - a) / n;

    for (int i = 0; i < n; ++i) // calculating sum
    {
        x = a + i * h;
        sum += cos(x * x) / (x + 1);
    }

    result = h * sum;
    return result;
}


float right_triangle_method()
{
    int n;
    float sum = 0;
    float a = 0.4;
    float b = 1.2;
    float h;
    float result;
    float x;

    std::cout << "Enter n for right-triangle method\n";
    std::cin >> n;

    h = (b - a) / n;

    for (int i = 1; i <= n; ++i) // calculating sum
    {
        x = a + i * h;
        sum += cos(x * x) / (x + 1);
    }

    result = h * sum;
    return result;
}

float central_triangle_method()
{
    int n;
    float sum = 0;
    float a = 0.4;
    float b = 1.2;
    float h;
    float result;
    float x;

    std::cout << "Enter n for central-triangle method\n";
    std::cin >> n;

    h = (b - a) / n;

    for (int i = 0; i < n; ++i) // calculating sum
    {
        x = a + i * h + h / 2;
        sum += cos(x * x) / (x + 1);
    }

    result = h * sum;
    return result;
}

float trapezium_method()
{
    int n;
    float sum = 0;
    float a = 0.4;
    float b = 1.2;
    float h;
    float result;
    float x;

    std::cout << "Enter n for central-triangle method\n";
    std::cin >> n;

    h = (b - a) / n;

    x = a;
    sum += cos(x * x) / (x + 1) / 2;
    x = a + n * h;
    sum += cos(x * x) / (x + 1) / 2;

    for (int i = 1; i < n; ++i) // calculating sum
    {
        x = a + i * h + h / 2;
        sum += cos(x * x) / (x + 1);
    }

    result = h * sum;
    return result;
}