Lab 2

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

int func();
float func1(float);
float integrate_me(float, float, int, int);

int main(void)
{
    float x0, xn, E, Itgr1, Itgr2, Itgr_final;
    int n, nc, ch, dowhl, clear=0;
    char Y_n;

    func();
    printf("\t\t%c%s%c\n", 179, "Hi there! Let's calculate the integral!", 179);
    func();

    do
    {
        if (clear>0)
        {
            getch();
            system("cls");
            clear=0;
        }
        dowhl=0;

        printf("Enter X0: ");
        scanf("%f", &x0);

        printf("Enter Xn: ");
        scanf("%f", &xn);

        printf("Enter the number(n) of intervals: ");
        scanf("%d", &n);

        printf("Enter riding error(E): ");
        scanf("%f", &E);

        printf("\n");

        printf("Select method:\n1.Left rectangles\n2.Right rectangles\n3.Trapezoids\n4.Simpson's\nAnswer : ");
        scanf("%d", &ch);

        Itgr1=integrate_me(x0, xn, n, ch);
        Itgr_final=Itgr1;
        if (Itgr1==999777)
        {
            clear=1;
            dowhl=1;
        }
        else
        {
                switch (ch)
                {
                    case 1:
                        printf("\nSelected method: Left rectangles\n\n");
                        break;
                    case 2:
                        printf("\nSelected method: Right rectangles\n\n");
                        break;
                    case 3:
                        printf("\nSelected method: Trapezoids\n\n");
                        break;
                    case 4:
                        printf("\nSelected method: Simpson's\n\n");
                        break;
                    default:
                        printf("Uncorrect answer\n");
                        return 1;
                        break;
                }

                Itgr2=integrate_me(x0, xn, n+2, ch);

                if (E>=fabsf(Itgr1-Itgr2))
                {
                    printf("%s%d%s\n\n", "Well, you enter n = ", n, "\nE is normal now!");
                }
                else
                {
                    printf("Bad news. E more than diving E\n");
                    nc=n;

                    do
                    {
                            nc+=2;
                            Itgr1=integrate_me(x0, xn, nc, ch);
                            Itgr2=integrate_me(x0, xn, nc+2, ch);
                    }
                     while(E<fabsf(Itgr1-Itgr2));

                     printf("%s%d%s\n\n", "If you will enter n = ", nc, " next time E will be normal!");
                }

                    printf("\t\t\t X0 = %.2f\n", x0);
                    printf("\t\t\t Xn = %.2f\n", xn);
                    printf("\t\t\t n = %d\n", n);

                    func();
                    printf("\t\t\t%s%.5f\n", " Integral = ", Itgr_final);
                    func();
        }

    printf("\nDo you want to start programm again?(Y/n)");
    fflush(stdin);
    scanf("%c", &Y_n);

    switch (Y_n)
        {
            case 'Y':
                dowhl=1; clear=1;
                printf("Ok, press something...");
                break;

            case 'y':
                dowhl=1; clear=1;
                printf("Ok, press something...");
                break;

            case 'N':
                return 0;


            case 'n':
                return 0;


            default:
                printf("Wrong answer. Programm will finish...\n");
                return 0;

            }

    }
    while (dowhl>0);

    return 0;
}

int func()
{
    int i;

    printf("\t\t%c ", 43);
    for (i=1; i<=19; i++) printf("%c ", 196);
    printf("%c\n", 43);
}

float integrate_me(float x0, float xn, int n, int ch)
{
    float h, S=0, Sn=0, I, x;

    h=(xn-x0)/n;
        switch(ch)
    {
    case 1:
        for (x=x0; x<=xn-h; x+=h)
            {
                S+=func1(x);
            }
        I=h*S;
        break;

    case 2:
        for (x=x0+h; x<=xn; x+=h)
            {
                S+=func1(x);
            }
        I=h*S;
        break;

    case 3:
        for (x=x0+h; x<=xn-h; x+=h)
            {
                S+=func1(x);
            }
        I=h*(func1(x0)/2+func1(xn)/2+S);
        break;

    case 4:
        if (n%2!=0)
        {
            printf("%s%c%d%c%s%c%d%c%s", "\nYour n(", 34, n, 34, ") is wrong!\nSimpson's method work for only paired numbers!(", 34, n+1, 34,  " for example)\nTry again!\n");
            return 999777;
        }
        else
        {
            for (x=x0+h; x<=xn-h; x+=2*h)
                {
                    S+=func1(x);
                }
            for (x=x0+2*h; x<=xn-2*h; x+=2*h)
                {
                    Sn+=func1(x);
                }
            I=h/3*(func1(x0)+4*S+2*Sn+func1(xn));
        }
        break;

    default:
        return 1;
        break;
    }
    return I;
}

float func1(float x)
{
    float F;

    F=x*pow(2.71828182,pow(x,2));
    // F=7/x;
    // + F=x/sqrt(pow(x,4)+16);
    return F;
}