#include <stdio.h>

float dotprod2(float x[2], float y[2]);

int main() {
    float a[2], b[2];
    float d;

    printf("Ax, Ay: ");
    scanf("%f, %f", &a[0], &a[1]);

    printf("Bx, By: ");
    scanf("%f, %f", &b[0], &b[1]);

    d = dotprod2(a, b);
    printf("Dot product: %f\n", d);
    return 0;
}

float dotprod2(float x[2], float y[2])
{
    return x[0]*y[0] + x[1]*y[1];
}