[C] JiMP 11.4

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

double f1(double x)
{
    return (2*x);
}

double f2(double x)
{
    return (x*x - 5*x + 4);
}

double f3(double x)
{
    return (3*x*x*x - 5*x - 1);
}

double bisection(double (*f)(), double floor, double ceiling, double approximation)
{
    while(abs(f((ceiling + floor)/2)) >= approximation)
    {
        double x = (floor + ceiling) / 2;
        if (f(floor) * f(x) <= 0)
        {
            ceiling = x;
        }
        else if ( f(ceiling) * f(x) <= 0 )
        {
            floor = x;
        }
    }
    return ((floor + ceiling)/2);
}

void menu()
{
    double floor, ceiling;
    int choice;

    printf("1. f(x) = 2x\n2. f(x) = x^2 - 5x + 4\n3. f(x) = 3x^2 - 5x - 1\n");
    scanf("%i", &choice);
    printf("\n");
    printf("Podaj dolna granice przedzialu: ");
    scanf("%lf", &floor);
    printf("\n");
    printf("Podaj gorna granice przedzialu: ");
    scanf("%lf", &ceiling);

    switch (choice)
    {
    case 1:
        printf("%lf", bisection(&f1, floor, ceiling, 1.e-5));
        break;
    case 2:
        printf("%lf", bisection(&f2, floor, ceiling, 1.e-5));
        break;
    case 3:
        printf("%lf", bisection(&f3, floor, ceiling, 1.e-5));
        break;
    }
}

int main()
{
    menu();
    return 0;
}