Metode Biseksi

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

double N,a,b,e,xr;
int i;

double f(double x){
    return exp(-x) - x;
}

void title(){
    puts("Praktikum Metode Numerik");
    puts("Metode Biseksi\n");
}

void input(){
    fflush(stdin);
    printf("Masukkan batas bawah : ");
    scanf("%lf",&a);
    fflush(stdin);
    printf("Masukkan batas atas : ");
    scanf("%lf",&b);
    fflush(stdin);
    printf("Masukkan toleransi : ");
    scanf("%lf",&e);

    fflush(stdin);
    printf("Masukkan jumlah iterasi : ");
    scanf("%lf",&N);
}

//Metode Biseksi
void metode(){

    if(f(a)*f(b)>0){
        puts("Tidak ada akar");
        return;
    }
    i = 0;
    printf("%-4s\t%-8s\t%-8s\t%-8s\t%-8s\t%-8s\t%-8s\n","i","a","b","xr","f(xr)","f(a)","Keterangan");
    do{
        i++;
        xr = (a + b)/2;
        printf("%-4d\t%-8lf\t%-8lf\t%-8lf\t%-8lf\t%-8lf\t%-8s\n",i,a,b,xr,f(xr),f(a),((f(a)*f(xr))<0)?"Berbeda tanda":"");

        if(f(a)*f(xr)<0){
            b=xr;
        }else
            a=xr;
    }while(fabs(b-a)>e && i<N);

    printf("Nilai xr = %lg\ndan f(xr) = %lg\n\n",xr,f(xr));
    printf("Nilai error nya : %lg\n",fabs(f(xr)));
}

char ulangi(){
    char opt;
    fflush(stdin);
    printf("Ulangi [y/t] ? :");
    scanf("%c",&opt);
    if(opt=='y'||opt=='Y')
        opt=1;
    else
        opt=0;
    return opt;
}

int main()
{
    title();
    do{
        input();
        metode();
    }while(ulangi());
    return 0;
}