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Ternary operator in C

  1. Feb 6, 2013 #1
    I was wondering if anyone knew if it is possible to construct an if else if with the ternary operator in C.

    I know that we can use it for if else, but what if you wanted multiple conditions for else if in your statement?

    Code (Text):
    printf("%d",(a>5)?1:(a<5)?0:10);
    //Just a silly example
    perhaps?
     
  2. jcsd
  3. Feb 6, 2013 #2

    jedishrfu

    Staff: Mentor

    I think you can do the nested ternary ops but you can't insert arbitrary java code in there. It must be an expression.

    You could use a user-defined boolean function for the condition and other functions for the result which in effect does the same thing but its probably harder to read in the long run for short if/else type work.

    double y = <some-user-boolean-function>(a,b,c) ? <some-user-function-returns-a-double>(a,b,c) : <some-other-user-function-that-returns-a-double(a,b,c);
     
    Last edited: Feb 6, 2013
  4. Feb 6, 2013 #3

    D H

    User Avatar
    Staff Emeritus
    Science Advisor

    Sure. It's just another operator. So,

    Code (Text):
    // Example 1, various assignments to x via conditional statements.
    if (cond1)
       x = val1;
    else if (cond2)
       x = val2;
    else if (cond3)
       x = val3;
    else
       x = val4;

    // Example 2, various assignments to y via conditional statements.
    if (cond1)
       if (cond2)
          if (cond3)
             y = val3;
          else
             y = val2;
       else
          y = val1;
    else
       y = val4;
    Writing these using the ternary operators:
    Code (Text):
    // Example 1, as a single assignment statement using multiple ternary operators
    x = cond1 ? val1 : cond2 ? val2 : cond3 ? val3 : val4;

    // Example 2, as a single assignment statement using multiple ternary operators
    y = cond1 ? cond2 ? cond3 ? val3 : val2 : val1 : val4;
    You may want to use parentheses. That ternary operator evaluates right to left combined with where it lives in the C-family precedence table can lead to some surprising interpretations by the compiler.
     
  5. Feb 6, 2013 #4

    I like Serena

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    Homework Helper

    Please consider that if you use such expressions in a software firm, it's likely that your colleagues will want to cut off your hands. ;)
     
  6. Feb 6, 2013 #5

    jedishrfu

    Staff: Mentor

    or better yet post t online for everyone to see:

    http://thedailywtf.com/
     
  7. Feb 6, 2013 #6

    D H

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    Staff Emeritus
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    Sure. In most cases (the vast, vast majority of cases) it's better to use if statements or a case statement instead of a complex expression using ternary operators. In many software firms chaining the ternary operator is verboten. Some places simply make the ternary operator verboten, period. Some people just don't grok functional programming so they ban its appearance in any form.

    There are a few cases where would I prefer the ternary operator, even chained. Clear, concise, functional. However, I can't use the ternary operator because I tend to work on projects that forbid its use. Rats! Double rats, as I am the author of the stupid coding standards on many of those projects. (I'm quite aware that quite a few people just can't grok functional programming.)
     
  8. Feb 6, 2013 #7

    jedishrfu

    Staff: Mentor

    If you like functional programming check out Scala, a better Java than Java. Its a combination of functional and OO programming styles.

    http://www.scala-lang.org/
     
  9. Feb 7, 2013 #8

    I like Serena

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    Functional programming... isn't that where you program fragments like
    Code (Text):

    (setq grok (?: cond1 val1 cond2 val2 cond3 val3 val4))
     
    just because you can?
     
    Last edited: Feb 7, 2013
  10. Feb 7, 2013 #9

    harborsparrow

    User Avatar
    Gold Member

    Just be aware that it is immoral to write code that is really tough for others to read. Agree with the "cut off your hands" comments above. :-)
     
  11. Feb 7, 2013 #10

    jedishrfu

    Staff: Mentor

    and then there's APL, a true write-only language of great power, simplicity and obfuscation that upon writing your program you can never ever hope to figure out what it does in finite time but at least you have the opportunity to rewrite it if you want.
     
  12. Feb 7, 2013 #11

    I like Serena

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    Homework Helper

    Ah yes, for those of us that think that
    Code (Text):

    (setq grok (?: cond1 val1 cond2 val2 cond3 val3 val4))
     
    is too obvious, we can simply write something like
    Code (Text):

    ⍋x
     
    to mean the same thing.
     
  13. Feb 7, 2013 #12

    D H

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    Staff Emeritus
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    Your syntax isn't quite right, and you're using an aspect of Lisp that isn't pure. Fixing both,
    Code (Text):
    (dosomethingwith (cond ((cond1) val1) ((cond2) val2) ((cond3) val3) (t val4)))
    Note the lack of the setq. That's verboten in pure Lisp. Something like C's i=i+1 doesn't make sense in purely functional languages.

    Functional programming requires a rather different outlook on programming.
     
  14. Feb 7, 2013 #13

    jedishrfu

    Staff: Mentor

    The best example for functional programming is in doing a generalized sorting algorithm where the comparison is left for the end programmer to provide. The comparison is placed in a function and the function is passed to the sort function and magically the data is sorted.

    Scala has all kinds of examples like this using closures. A closure is a kind of function that is passed to one of many collection iterators that Scala has in its arsenal of programming constructs.
     
  15. Feb 8, 2013 #14

    D H

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    Staff Emeritus
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    C++ also has functional programming features. There's std::sort, for example. C++11 takes C++ much further along the road toward being a functional language. Lambda expressions, bindings, currying, ...
     
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