Before writing the C program to check whether the triangle is isosceles, we should know the properties of equilateral triangles. In geometry, an isosceles triangle is a triangle that has two sides of equal length.

#include <stdio.h>

int main()

{

int side1, side2, side3;

//Get sides of a triangle from the user

printf(“Enter sides of triangle\n”);

scanf(“%d%d%d”, &side1,&side2,&side3);

if((side1==side2) || (side1==side3) || (side2==side3))

{

//two sides are equal, so isosceles triangle

printf(“isosceles triangle.\n\n”);

}

else

{

printf(“Not a isosceles triangle.\n\n”);

}

return 0;

}

**Output:**