Find Line Passing Through 2 Points in C++

In this problem, we are given coordinates two points A and B on the coordinate plane. Our task is to create a program to find line passing through 2 Points in C++.

Problem Description

To find the line, we need to use the equation of the line and put the solution using the coordinates.

Let’s take an example to understand the problem−

Input: A = (3, 3) B = (6, 1) 

Output: 2x + 3y = 15

Solution Approach

To find the equation of the line, we will use the general equation of line −

ax + by = c

This has to be satisfied by both the points A(x1, y1) and B(x2, y2)

The will make the equations,

ax1 + by1 = c

ax2 + by2 = c

Now, as c is common for both the equations we have

ax1 + by1 = ax2 + by2

=> ax1 - ax2 = by2 - by1

On equating we get,

$$a = (y2 - y1)$$ $$b = (x1 - x2)$$

c will be found using the equation,

$$ax1 + by1 = c$$

So, this is the equation for the equation of the line,

$$a = (y2 - y1)$$ $$b = (x1 - x2)$$ $$c = ax1 + by1$$

Example

 Live Demo

#include <iostream> using namespace std;
void findLine(int points[2][2]) {
   int a = points[1][1] - points[0][1];
   int b = points[0][0] - points[1][0]; int c = a*points[0][0] + b*points[0][1];
   cout<<"("<<a<<"x) + ("<<b<<"y) = ("<<c<< 
}
int main() {
   int points[2][2] = {{5, 9}, {1, 4}}; cout<<"The equation of line is "; findLine(points);
   return 0;
}

Output

The equation of line is (-5x) + (4y) = (11)