What does '?' do in C++?


Question

int qempty()
{
    return (f == r ? 1 : 0);
}

In the above snippet, what does "?" mean? What can we replace it with?

1
64
9/7/2014 9:55:17 AM

Accepted Answer

This is commonly referred to as the conditional operator, and when used like this:

condition ? result_if_true : result_if_false

... if the condition evaluates to true, the expression evaluates to result_if_true, otherwise it evaluates to result_if_false.

It is syntactic sugar, and in this case, it can be replaced with

int qempty()
{ 
  if(f == r)
  {
      return 1;
  } 
  else 
  {
      return 0;
  }
}

Note: Some people refer to ?: it as "the ternary operator", because it is the only ternary operator (i.e. operator that takes three arguments) in the language they are using.

112
4/27/2009 9:23:10 PM

This is a ternary operator, it's basically an inline if statement

x ? y : z

works like

if(x) y else z

except, instead of statements you have expressions; so you can use it in the middle of a more complex statement.

It's useful for writing succinct code, but can be overused to create hard to maintain code.


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