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.

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

Triangle is equilateral triangle

Required knowledge

Basic programming, If else, Basic Mathematics

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.

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 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 either a == b or a == c or b == c.
• A triangle is said Scalene Triangle, if none of its sides are equal.

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 a, b and c.
2. Check if a == b and b == c. Then it is an equilateral triangle.
3. If it is not an equilateral triangle. Then check if a == b or a == c or b == c. Then it is isosceles triangle.
4. If it is neither equilateral nor isosceles triangle then it must be scalene triangle.

Let us implement the logic using C program

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 a, b, c; //a, b, c are three sides of a triangle

    /* Reads all sides of a triangle */
    printf("Enter three sides of triangle: ");
    scanf("%d%d%d", &a, &b, &c);

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

    return 0;
} 

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

Happy coding ;)