Sequence of if-else if in C

Question

I' using the following logic for testing whether the triangle is isosceles, equilateral, scalene or right angled.

if (side1 == side2 || side2 == side3 || side1 == side3)
    printf("Isosceles triangle.");
else if (side1 == side2 && side2 == side3 && side3 == side1)
    printf("equilateral triangle");

I get the output for sides 3 3 3 as isosceles but not equilateral but when I interchange the logic that is write the logic of equilateral first I get equilateral. I can't understand what's happening?

Answer 1

You shouldn't use else in this case.

Code:

if (condition)
     code
else if (condition2)
     code2

Checks if condition is true. If so it executes code. Only if condition is false, condition2 is checked and code2 could be executed.

Answer 2

Your code "checks" the second if only when the first if is false.
logically the second if can be true only if the first if is true...

I would change the code to:

if (side1 == side2 || side2 == side3 || side1 == side3)
{
    printf("Isosceles triangle.");
    if (side1 == side2 && side2 == side3 && side3 == side1)
        printf("equilateral triangle");
}