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

Write a C program to input sides of a triangle and check whether a triangle is equilateral, scalene or isosceles triangle using if else. 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`

## Properties of triangle

• A triangle is said Equilateral Triangle, if all its sides are equal. If a, b, 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, 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

Step by step descriptive logic to classify triangle as equilateral, scalene or isosceles triangle.

1. Input sides of a triangle from user. Store it in some variables say side1, side2 and side3.
2. Check `if(side1 == side2 && side2 == side3)`, then the triangle is equilateral.
3. If it is not an equilateral triangle then it may be isosceles. Check `if(side1 == side2 || side1 == side3 || side2 == side3)`, then triangle is isosceles.
4. If it is neither equilateral nor isosceles 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 any 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 😉 