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I have just started my C++ lecture class. And the teacher has given us the following assignment.

Write a program that determines whether a number is even or odd.

The logic I would use for the program is.

  1. Get input a.
  2. Store a % 2 as b.
  3. If b is 0, then a is even, else a is odd.

The catch though, is that we have to write the program without the use of a if-else statement.

I have been thinking on how to approach the problem for the past few hours, but I have no clue what to do. Any hints or suggestions?

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Maybe the ? operator is your friend? –  Giorgio Jun 2 '12 at 17:00
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@Giorgio I'd consider that an if/else. –  Andrew Finnell Jun 2 '12 at 17:00
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@Giorgio - that's still an if/else –  ChrisF Jun 2 '12 at 17:01
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This is a silly problem with silly solutions that's way too localized to help anyone else. –  DeadMG Jun 2 '12 at 17:48
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@ChrisF Belongs on SO? –  Dynamic Jun 2 '12 at 20:06
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closed as too localized by DeadMG, Mark Trapp, gnat, ChrisF Jun 3 '12 at 19:52

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2 Answers

Here's one way to do it:

int a;
/* get input and place into a... */
int b = a % 2;
const char *values[] = {"even", "odd"};
const char *result = values[b];
/* output result */

Note that the ternary-operator (?:) is not using if-else in the syntactic sense, although it would be compiled down to the same machine instructions.

Ditto, you could use the condition of a while loop to check what you need. Simply break out of it, and that too should be optimized down to the same machine instructions. The same would go for using a switch, which might've been what your instructor was trying to get at.

If you want to make better use of data structures, you could use a map structure (also known as dictionaries and associative arrays) to give you a generalization against many cases. The values stored in the map could even be function pointers or functors (in your simpler case, a string would be sufficient as the value).

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Is char *values[] = {"even", "odd"}; legal? I thought converting string literals to char* was deprecated. –  Pubby Jun 2 '12 at 19:17
    
@Pubby, of course it's legal. I don't think they deprecated char *argv[]. =P –  Bryan Dunsmore Jun 2 '12 at 19:29
    
This is exactly what I would do. However, I think Pubby's point is that the char pointers should have been const char pointers. –  user16764 Jun 2 '12 at 19:49
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@dunsmoreb char *argv[] as an argument is equivalent to char **argv and there's no string literal involved so it's irrelevant. user16764 is correct in that const is correct here. –  Pubby Jun 2 '12 at 20:18
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Thanks! I added in the const. My only defense is that it was pseudo code! :-) You don't want to do all of the HW assignment. –  Macneil Jun 3 '12 at 3:19
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a % 2 already tells you whether it's even or odd.

std::cout << std::boolalpha << a % 2; // outputs true or false
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No. It tells you whether it is true or false. –  Bryan Dunsmore Jun 2 '12 at 17:54
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@dunsmoreb: Which is exactly the same thing. "Is a odd?" "true/false". –  DeadMG Jun 2 '12 at 17:56
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The output would be more like: 5 false. –  Bryan Dunsmore Jun 2 '12 at 18:04
    
@dunsmoreb: Why would it be 5 false and not just true? –  DeadMG Jun 2 '12 at 22:06
    
For one, five is odd. =P And two, I'm assuming the input would be echoed. –  Bryan Dunsmore Jun 2 '12 at 22:07
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