Two points such as (x1,y1) and (x2,y2) for how we can find the straight line equation such type of program are described here.

Find Equation

#include <stdio.h>
int main()
{
    int p[2],q[2],x,i,j,k;
    float m,y;
    printf("Enter your two points : \n");
    for(i=1;i<=2;i++)
    {
    printf("x[%d] : ",i);
    scanf("%d", &p[i]);
    printf("y[%d] : ",i);
    scanf("%d", &q[i]);
    }
    printf("Your putting two value are : \n\n");
    for(i=1;i<=2;i++)
    printf("x[%d] : %d \t y[%d] : %d\n",i,p[i],i,q[i]);
    j=q[2]-q[1];
    k=p[2]-p[1];
    m=j/k;
    y=q[1]-m*p[1];
    if(j==k)
    {
    j=k=1;
    printf("\n\nYour equation are : \n");
    printf("\t\ty=%dx+%.1f\n\n",j,y);
    }
    else
    {
        printf("\n\nYour equation are : \n");
        printf("\t\ty=%d/%dx+%.1f\n\n",j,k,y);
    }

    return 0;
}