Ternary operator mql4

I have a question in regards to the understanding ternary operator

double true_range = (High==Low)?0:(Close-Open)/(High-Low);

The above entry is equivalent to the following:

double true_range;
else true_range=(Close-Open)/(High-Low);

but if I removed the variable "true_range " and use the “Alert” function as follows:

Alert ((High==Low)?0:(Close-Open)/(High-Low)); it still works but when I do the same using " if" it does not work

Can someone clarify the reason?

Thanks in advance