Numerical Methods:Fitting the curve of the form y = a + bx using least square method in C

Source Code : 

///Curve fitting of a straight line of the form y = a + bx
#include<stdio.h>
#include<math.h>
int main(){
    int ax[20], ay[20], i, n;
    int sum_x = 0, sum_xy = 0, sum_x2 = 0, sum_y = 0 ;
    float a , b;
    printf("Enter no of records: ");
    scanf("%d", &n);
    printf("Enter Data: ");
    printf("\nX       Y\n");
    for(i = 0; i < n; i++){
        scanf("%d%d", &ax[i], &ay[i]);
    }
    for(i = 0; i < n; i++){
        sum_x += ax[i];
        sum_y += ay[i];
        sum_xy += ax[i] * ay[i];
        sum_x2 += pow(ax[i], 2);
    }
    b = (n*sum_xy - sum_x*sum_y)/(n*sum_x2 - pow(sum_x,2));
    a = (sum_y - b*sum_x)/n;
    printf("\na = %.3f    b = %.3f", a, b);
    printf("\nThe Equation is %.3f + %.3fX\n\n", a, b);
    return 0;
}