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

## Required knowledge

Basic C programming, Relational operators, Logical operator, If else

## 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.

- Input sides of a triangle from user. Store it in some variables say
`side1`,`side2`and`side3`. - Check
`if(side1 == side2 && side2 == side3)`

, then the triangle is equilateral. - If it is not an equilateral triangle then it may be isosceles. Check
`if(side1 == side2 || side1 == side3 || side2 == side3)`

, then triangle is isosceles. - 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 😉

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