Comparing several values.

**msh** · 05-20-2010

Never thought I'd be asking a "homework question", but this qualifies as one, since it is from the chapter review section of the book I'm reading (C Plus Primer, 5th ed., for the curious).

"Write a function that returns the largest of three integer arguments."

For two values it'd be an easy return a > b ? a : b;

For three (or more, I suppose), I came up with this. Could someone tell me if I'm over-engineering or give me a pointer to a better solution? I know that I sometimes tend to miss the obvious one.

Code:

int compare(int a, int b, int c) {
  int max = 0;
  int tmp[3] = {a, b, c};
  
  for (int i = 0; i < 3; i++) {
    if (tmp[i] > max) {
      max = tmp[i];
    }
  }
  
  return max;
}

Thanks for you time!

**laserlight** · 05-20-2010

I suspect that the author was expecting a solution using a series of if-else statements. As for your loop: it works correctly unless all of the arguments are negative. You should actually set max's value to be INT_MIN, or to be one of the arguments.

**msh** · 05-20-2010

Originally Posted by laserlight

I suspect that the author was expecting a solution using a series of if-else statements. As for your loop: it works correctly unless all of the arguments are negative. You should actually set max's value to be INT_MIN, or to be one of the arguments.

Thanks for the spot! I hadn't thought of the all-negative case.

I took a peek at the answers section and, true enough, if-else series was the expected solution, which I found a little disappointing.

**Driver** · 05-20-2010

The negative case is handled easily enough by priming max to the first value in the array rather than assuming zero:

Code:

int compare(int a, int b, int c) {
  int tmp[3] = {a, b, c};
  int max = tmp[0];

  for (int i = 1; i < 3; i++) {
    if (tmp[i] > max) {
      max = tmp[i];
    }
  }
  
  return max;
}

It starts by assuming the first element in the array is the maximum, then going from there. Note how the iterator now starts from array index 1 now, as the 0'th has been catered for already by that stage.

If it's a simple test, then you can either use if...else or a single-line ternary operator to do it:

Code:

return a > b ? (a > c ? a : c) : (b > c ? b : c);

but that's not so readable as if...else

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