Question

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Order of condition checking?

When i read some source codes, the if statement is coded in this way,

if (1 == a) {
   ...
}

instead of

if (a == 1){
    ...
}

I read a programming book about the advantage of this way, but cannot remember exactly what it is about. Any one know about this ?

(Sorry if this question disturbs you 🙂 )

Answer 1

The advantage is compiler will tell you that error right away. For example, a = 1 will compile but will produce an error at run time whereas 1 = a will produce an error at compile time since 1 is not a valid lvalue.

Example: this will produce an error right away:

       int a = 0;
       if(1 = a) {
        print("test");
       }

Whereas this will compile (warnings may be produced depending on the compiler) but it will cause issues at run time.

       int a = 0;
       if(a = 1) {
           print("test");
       }

The main idea here is to make certain that you are using == in a condition instead of =.

That being said every modern compiler (ie. Eclipse) will treat the above as an error now. So it’s not as big of a deal as it used to back in the notepad and vi days (in my opinion). I personally prefer the a == 1 since that seems more readable to me.