workshop 9 - bai 2 - HQT

#include <stdio.h>
#define MAX 100

int main(){
    int sum = 0;
    int x[MAX], y[MAX];
    double mx=0.0, my=0.0;
    int i = 0;
    char filename[80];

    printf("Regression Analysis Calculator\n");
    printf("==============================\n");

    printf("Enter the name of the data file: "); scanf("%s",filename);
    FILE * f;
    f = fopen(filename, "r");
    if (f == NULL){
        printf("Cannot open file\n");
        return;
    }
    while (!feof(f)){
        fscanf(f,"%d",&x[sum]);
        fscanf(f,"%d",&y[sum]);
        mx += x[sum]; my +=y[sum];
        sum++;
    }
    mx /= n;
    my /= n;
    fclose(f);

    // find slope(t)
    float t = 0.0;
    float ts =0.0, ms = 0.0;
    for(i=0; i<sum; i++){
        ts += (x[i] - mx)*(y[i] - my);
        ms += (x[i] - mx)*(x[i] -mx);
    }
    t = ts/ms;

    // y-intercept (b)
    float b = my - t*mx;

    // find sx and sy
    float sx = 0.0, sy=0.0;
    for(i=0; i<sum; i++){
        sx +=  x[i]*x[i];
        sy +=  y[i]*y[i];
    }

    // d : standard deviation
    float dx = ( sx / n ) - mx*mx;
    float dy = ( sy / n ) - my*my;

    // correlation coefficient : r = { [ (x1y1) + (x2y2) + ... + (xnyn) ] / n - mx my} / [ dx dy ]
    float r = 0.0;
    float p1 = 0.0;
    for(i=0; i<sum; i++){
        p1 += x[i]*y[i];
    }
    r = (p1/sum - mx*my) / (dx*dy);

    printf("The number of data values read from this file was %d\n", sum);
    printf("The slope of the least squares fit is : %f",t);
    printf("The y-intercept of the least squares fit is : %f",b);
    printf("The correlation coefficient is: %f", r);

}