Metode Newton Raphson

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

double x1,x2,er,e;
int N;

double f1(double x)
{
    return (1+exp(-x));
}
double f(double y)
{
    return y-exp(-y);
}

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

void input(){
    fflush(stdin);
    printf("Pendekatan awal : ");
    scanf("%lf",&x1);
    fflush(stdin);
    printf("Masukkan toleransi : ");
    scanf("%lf",&e);

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

//Newton Raphson
void metode()
{
    int i=0;
    printf("%-4s %-20s %-20s %-8s\n","i","x","f(x)","f'(x)");
    do
    {
        x2=x1-(f(x1)/f1(x1));
        printf("%-4d %-20lg %-20lg %-8lg \n",i,x1,f(x1),f1(x1));
        er=fabs(f(x1));
        x1=x2;
        i++;
    }
    while(i<N && er>e);
    printf("akar : %lg\n",x1);
}
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;
}