C program to check whether triangle is equilateral, scalene or isosceles

Write a C program to check whether a triangle is equilateral, scalene or isosceles triangle using if else. Program to enter sides of a triangle and classify triangle as Equilateral, Scalene or Isosceles triangle using if else in C. How to check whether a triangle is equilateral, scalene or isosceles triangle in C programming. Logic to classify triangles as equilateral, scalene or isosceles triangle if sides are given in C program.

Example
Input

Input first side: 30
Input second side: 30
Input third side: 30

Output

Triangle is equilateral triangle

Required knowledge

Basic programming, If else, Basic Mathematics

Properties of triangle

  • A triangle is said Equilateral Triangle, if all its sides are equal. If a, b and c are three sides of triangle. Then, the triangle is equilateral only if a == b == c.
  • A triangle is said Isosceles Triangle, if its two sides are equal. If a, b and c are three sides of triangle. Then, the triangle is isosceles if either a == b or a == c or b == c.
  • A triangle is said Scalene Triangle, if none of its sides are equal.

Logic to check equilateral, scalene or isosceles triangle

Before we actually dive into the logic and programming section of this exercise. Let us first learn some basic properties of triangle and learn how to differentiate between triangles.

Below is the step by step descriptive logic to classify triangle as equilateral, scalene or isosceles triangle.

  1. Read three sides of a triangle and store it in some variable say side1, side2 and side3.
  2. Triangle is equilateral if side1 == side2 and side2 == side3.
  3. If it is not an equilateral triangle. The triangle is isosceles if side1 == side2 or side1 == side3 or side2 == side3.
  4. If it is neither equilateral nor isosceles triangle then it scalene triangle.

Program to check equilateral, scalene or isosceles triangle

/**
 * C program to check whether a triangle is Equilateral, Isosceles or Scalene
 */

#include <stdio.h>

int main()
{
    int side1, side2, side3;

    /* Input sides of a triangle */
    printf("Enter three sides of triangle: ");
    scanf("%d%d%d", &side1, &side2, &side3);

    if(side1==side2 && side2==side3) 
    {
        //If all sides are equal
        printf("Equilateral triangle.");
    }
    else if(side1==side2 || side1==side3 || side2==side3) 
    {
        //If two sides are equal
        printf("Isosceles triangle.");
    }
    else 
    {
        //If none sides are equal
        printf("Scalene triangle.");
    }

    return 0;
}

Output

Enter three sides of triangle: 30
30
30
Equilateral triangle.

Happy coding 😉

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