Lagrange

#include < stdio.h > #define FMT "%-10.5g"#define N 3 typedef float DBL[N];float Lag(DBL x, DBL f, int n, float xx) {    int k,    j;    float r,    s = 0.0;    for (k = 0; k <= n; k++) {        r = 1.0;        for (j = 0; j <= n; j++) if (j != k) r *= (xx - x[j]) / (x[k] - x[j]);        s += f[k] * r;    }    return s;}void main() {    int i;    DBL x,    f;    float xx;    printf("\n");    for (i = 0; i < N; i++) {        printf("x[%d]=", i);        scanf("%f", x + i);        printf("f(%d)=", i);        scanf("%f", f + i);    }    printf("x=");    scanf("%f", &xx);    xx = Lag(x, f, N - 1, xx);    printf("\nf(x)=");    printf(FMT, xx);}