INCREMENTING / DECREMENTING OPERATORS

Previously, we have added 1 to a variable by writing

   A = A + 1;
or
   A += 1;

C++ provides an operator which will automatically add 1 to a variable: ++ .  We call ++ the incrementing operator since it increments a variable by one. To add one to A we can write:

   A++;
or
   ++A;

Notice that you can have the ++ before or after the variable.  If you place the operator after the variable we call it a postfix operator (post as in after).  Conversely, the incrementing operator placed before the variable is referred to as a prefix operator (pre as in before).

It is important to note that all provided examples can be applied to the decrementing operator (--) as well.  As you may have guessed, this operator subtracts 1 from the target variable.
 

Effects

The prefix operator
  1) increments/decrements the variable
  2) executes the statement

The postfix operator
  1) performs the operation
  2) executes the statement
 

Consider a code example and its output to demonstrate the difference.

#include <iostream.h>

int main() {
  int i = 1, Result;

  cout << "i: " << i << endl;
  Result = i++;
  cout << "Result: " << Result << "; i: " << i << endl;

  cout << "i: " << i << endl;
  Result = ++i;
  cout << "Result: " << Result << "; i: " << i << endl;

  return 0;
}

Output:

  i: 1
  Result: 1; i: 2
  i: 2
  Result: 3; i: 3

You should examine this program step by step to verify how the operators work.

To test your understanding, what is the output of the following code?

  int i = 1;
  cout << (++i)++ << endl;
  cout << i << endl;

To verify your answer, copy and paste this in a program and execute it.
 

I advise that you choose either the prefix or postfix operator and stick with it.
 

We will do many examples pertaining to these operators.