Sometimes, you’ll have a scenario with two variables, and you need to use one of them based on a simple test. Rather than a long and awkward if / else statement, C allows the use of the ? : form. It is perfectly acceptable to write:
int i,j,k,l;
...
i = (j > 5? k : l)which will set i to k if j is greater than 5, and l otherwise.
Another common use is [sf]?printf statements:
printf("The test %s\n",(status == OK) ? "passed" : "failed");However, one can’t use it to handle selective assignments. The following code is illegal:
int i,j,k;
...
((i>5) ? j : k) = 5;This cannot be used to choose whether j or k is set to 5.
There is, however a way this can be done. Using pointer, we can select which one to deference:
*((i>5) ? &j : &k) = 5;This will work.
2 responses to “Conditional Assignments”
Do you ever actually use the famous trinary operator
… in code that anyone else is going to read/maintain?
I’m no big-time C hacker, but C++ code is a major part of my job, and it seems to me that if/else is a great deal more readable, even for little one- or two-liners. The main utilities of ?/:, it seems to me, are to help you save a few bytes on the hard drive where you keep your code and to keep the ? and : characters from feeling bad for being left out of the language specification.
I use it (then again, I’m a big time C hacker).
This little trick is rather useless, I admit, but a fun piece of trivia (I’m interviewing some students now for a position, and so I’ve been collecting fun bits of trivial trivia). If you prefer if/else, be my guest… it is a little more readable, but sometimes, you have a long and complex statement that you really don’t want to rewrite, or a print statement that needs some text:
max = (i>j) ? i : j;
instead of:
I assume you also prefer brackets, which means you might have:
Is that really better? Sometimes, cleaner code is when you can see the entire thing on one screen, instead of having a really long spread out function.
Also, compare:
with