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

void mkdiff(int n,double X[n],double Y[n],
    double P[n+1][n]){
    for(int i=0;i<n;i++){
        P[0][i]=X[i]; P[1][i]=Y[i];
    }
    for(int j=2;j<=n;j++){
        for(int i=0;i<=n-j;i++){
            P[j][i]=P[j-1][i+1]-P[j-1][i];
        }
    }
}
double evalP(int n,double P[n+1][n],
    double h,double x){
    double z=1.0,r=z*P[1][0];
    for(int j=2;j<=n;j++){
        z*=(x-P[0][j-2])/((j-1)*h);
        r+=z*P[j][0];
    }
    return r;
}
void printP(int n,double P[n+1][n]){
    for(int i=0;i<n;i++){
        for(int j=0;j<=n;j++){
            printf("%g ",P[j][i]);
        }
        printf("\n");
    }
}
#define N 4
#define H 1.0
double X[N]={1, 2, 3, 4};
double Y[N]={-1,2,4,-3};
double P[N+1][N];
int main(){
    mkdiff(N,X,Y,P);
//  printP(N,P);
    for(int k=0;k<50;k++){
        double x=k/10.0;
        printf("%g %g\n",x,evalP(N,P,H,x));
    }
    return 0;
}