Program to implement the linear regression algorithm in C.

#include<stdio.h>
#include<conio.h>
#include<math.h>
#include<string.h>

float mean(float *a, int n);
void deviation(float *a, float mean, int n, float *d, float *S);

void main()
{
float a[20],b[20],dx[20],dy[20];
float sy=0,sx=0,mean_x=0,mean_y=0,sum_xy=0;
float corr_coff=0,reg_coff_xy=0, reg_coff_yx=0;
char type_coff[7];
int n=0,i=0;

clrscr();

printf("Enter the value of n: ");
scanf("%d",&n);
printf("Enter the values of x and y:\n");
for(i=0;i<n;i++)
scanf("%f%f",&a[i],&b[i]);
mean_x=mean(a,n);
mean_y=mean(b,n);
deviation(a,mean_x,n,dx,&sx);
deviation(b,mean_y,n,dy,&sy);

for(i=0;i<n;i++)
sum_xy=sum_xy+dx[i]*dy[i];
corr_coff=sum_xy/(n*sx*sy);
printf("Enter the type of regression coefficient as 'x on y' or 'y on x': ");
fflush(stdin);
gets(type_coff);

if(strcmp(type_coff,"x on y")==1)
{
reg_coff_xy=corr_coff*(sx/sy);
printf("\nThe value of linear regression coefficient is %f",reg_coff_xy);
}
else if(strcmp(type_coff,"y on x")==1)
{
reg_coff_yx=corr_coff*(sy/sx);
printf("\nThe value of linear regression coefficient is %f",reg_coff_yx);
}
else
printf("\nEnter the correct type of regression coefficient.");
getch();
}


float mean(float *a, int n)
{
float sum=0, i=0;
for(i=0;i<n;i++)
sum=sum+a[i];
sum=sum/n;
return (sum);
}

void deviation(float *a, float mean, int n, float *d, float *s)
{
float sum=0,t=0;
int i=0;
for(i=0;i<n;i++)
{
d[i]=a[i]-mean;
t=d[i]*d[i];
sum=sum+t;
}
sum=sum/n;
*s=sqrt(sum);
}
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