LaGrange.c

#include "stdio.h"
#include "math.h"

float calculateX(float xFrom, float i, float step) {
    return xFrom + i*step;
}
float yFormula(float x) {
    return exp(-(x - 2) * (x - 2));
}

void printLBase(int i, int n, float xFrom, float step) {
    printf("(");
    for (int j = 0; j <= n; j++) {
        if (j == i)
            continue;
        printf("(x - %f)", calculateX(xFrom, j, step));
    }
    printf(")/(");
    for (int j = 0; j <= n; j++) {
        if (j == i)
            continue;
        printf("(%f - %f)", calculateX(xFrom, i, step), calculateX(xFrom, j, step));
    }
    printf(")");
}

int main(int argc, char** argv) {
    float xFrom = 2;
    float xTo = 4;
    float step = 0.2;

    int n = (int)((xTo-xFrom) / step);

    printf("L(x) = ");
    for (int i = 0; i <= n; i++) {
        printLBase(i, n, xFrom, step);
        if (i < n)
            printf(" + ");
    }

    return 0;
}