C program to check triangle is Equilateral, Isosceles or Scalene

by devang · February 11, 2016

Before going to the program to check triangle is Equilateral, Isosceles or Scalene first let us understand what is a Equilateral, Isosceles or Scalene Triangle?

Equilateral Triangle:

A Triangle is said to be an Equilateral Triangle if all the three sides are equal.

Isosceles Triangle:

A Triangle is said to be an Isosceles Triangle if its two side are equal.

Scalene Triangle:

A Triangle is said to be an Scalene Triangle if all the three sides are different.

Program code to check Equilateral, Isosceles or Scalene Triangle:

#include<stdio.h>
#include<conio.h>

void main()
{
    int a, b, c;
    clrscr();
    
    printf("\n\n Enter three sides of triangle: ");
    scanf("%d %d %d", &a, &b, &c);
    
    if(a<=0 || b<=0 || c<=0)
    {
        printf("\n INVALID INPUT");
    }
    else if(a==b && b==c)
    {
        printf("\n Equilateral Triangle");
    }
    else if(a==b || a==c || b==c)
    {
        printf("\n Isosceles Triangle");
    }
    else
    {
        printf("\n Scalene Triangle");
    }
    getch();
}

Step by Step working of the above Program Code:

For Invalid Input:

Let us assume that the user enters the three sides of triangle as 4 0 4.
So it assigns the value of a=4, b=0, c=4.
a<=0 or b<=0 or c<=0 (4<=0 or b<=0 or c<=0) if condition is true
- So it prints as INVALID INPUT.
Thus the program execution is completed.

For Equilateral Triangle:

Let us assume that the user enters the three sides of triangle as 10 10 10.
So it assigns the value of a=10, b=10, c=10.
a<=0 or b<=0 or c<=0 (10<=0 or 10<=0 or 10<=0) if condition is false
- So it goes to next else if part.
a==b and b==c (10==10 and 10==10) if condition is true
- So it prints as Equilateral Triangle.
Thus the program execution is completed.

For Isosceles Triangle:

Let us assume that the user enters the three sides of triangle as 30 20 30.
So it assigns the value of a=30, b=20, c=30.
a<=0 or b<=0 or c<=0 (30<=0 or 20<=0 or 30<=0) if condition is false
- So it goes to next else if part.
a==b and b==c (30==20 and 20==30) if condition is false
- So it goes to next else if part.
a==b or a==c or b==c (30==20 or 30==30 or 20==30) if condition is true
- So it prints as Isosceles Triangle.
Thus the program execution is completed.

For Scalene Triangle:

Let us assume that the user enters the three sides of triangle as 10 20 30.
So it assigns the value of a=10, b=20, c=30.
a<=0 or b<=0 or c<=0 (10<=0 or 20<=0 or 30<=0) if condition is false
- So it goes to next else if part.
a==b and b==c (10==20 and 20==30) if condition is false
- So it goes to next else if part.
a==b or a==c or b==c (10==20 or 10==30 or 20==30) if condition is false
- So finally it goes to else part and prints as Scalene Triangle.
Thus the program execution is completed.