# C Exercises: Check two lines are parallel or not

## C Basic Declarations and Expressions: Exercise-138 with Solution

Write a C program to test whether two lines are parallel or not. The four points are P(x1, y1), Q(x2, y2), R(x3, y3) and S(x4, y4), check PQ and RS are parallel are not.

Input:

−100 <= x1, y1, x2, y2, x3, y3, x4, y4 <= 100

Each value is a real number with at most 5 digits after the decimal point.

**Sample Solution:**

**C Code:**

```
#include <stdio.h>
main() {
// Variable declarations
double x1, x2, y1, y2, x3, y3, x4, y4;
int i, n;
// Getting user input for coordinates
printf("Input P(x1,y1):\n");
scanf("%lf %lf", &x1, &y1);
printf("\nInput P(x2,y2):\n");
scanf("%lf %lf", &x2, &y2);
printf("\nInput P(x3,y3):\n");
scanf("%lf %lf", &x3, &y3);
printf("\nInput P(x4,y4):\n");
scanf("%lf %lf", &x4, &y4);
// Checking if lines PQ and RS are parallel
if ((x1 == x2) && (x3 == x4))
printf("\nPQ and RS are parallel!\n");
else if ((x1 == x2) || (x3 == x4))
printf("\nPQ and RS are not parallel!\n");
else if (((y1 - y2) / (x1 - x2) - (y3 - y4) / (x3 - x4)) == 0.0)
printf("\nPQ and RS are parallel!\n");
else
printf("\nPQ and RS are not parallel!\n");
return (0); // End of the program
}
```

Sample Output:

Input P(x1,y1): 5 7 Input P(x2,y2): 3 6 Input P(x3,y3): 8 9 Input P(x4,y4): 5 6 PQ and RS are not parallel!

**Flowchart:**

**C programming Code Editor:**

**Previous:** Write a C program to check if a point (x, y) is within a triangle or not. The triangle has formed by three points.

**Next:** Write a C program to find the maximum sum of a contiguous subsequence from a given sequence of numbers a1, a2, a3, ... an ( n = number of terms in the sequence).

**What is the difficulty level of this exercise?**

Test your Programming skills with w3resource's quiz.

**Weekly Trends**- Python Interview Questions and Answers: Comprehensive Guide
- Scala Exercises, Practice, Solution
- Kotlin Exercises practice with solution
- MongoDB Exercises, Practice, Solution
- SQL Exercises, Practice, Solution - JOINS
- Java Basic Programming Exercises
- SQL Subqueries
- Adventureworks Database Exercises
- C# Sharp Basic Exercises
- SQL COUNT() with distinct
- JavaScript String Exercises
- JavaScript HTML Form Validation
- Java Collection Exercises
- SQL COUNT() function
- SQL Inner Join