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Examples of if statements

The following if statement adds x to a variable sum if x is positive:

if (x > 0.0)
  sum += x;

The following if statement also adds x to sum but in addition it adds 1 to a count of positive numbers held in the variable poscount:

if (x >= 0.0)
  {
    sum += x;
    poscount++;
  }
Note the use of the addition/assignment operator, and of the increment operator. Note how in the second example a compound statement has been used to carry out more than one operation if the condition is true. If this had been written as follows:
if (x >= 0.0)
   sum += x;
   poscount++;
then if x was greater than zero the next statement would be executed, that is x would be added to sum. However the statement incrementing poscount would then be treated as the next statement in the program, and not as part of the if statement. The effect of this would be that poscount would be incremented every time, whether x was positive or negative.

The statements within a compound statement can be any C++ statements. In particular, another if statement could be included. For example, to print a message if a quantity is negative, and a further message if no overdraft has been arranged:

if ( account_balance < 0 )
  {
    cout << "Your account is overdrawn.  Balance "
         << account_balance << endl;
    if ( overdraft_limit == 0 )
      cout << "You have exceeded your limit. << endl;
  }

In this case, the same effect could have been achieved using two if statements, and a more complex set of conditions:

if ( account_balance < 0 )
  cout << "Your account is overdrawn.  Balance "
       << account_balance << endl;
if ( account_balance < 0 && overdraft_limit == 0 )
  cout << "You have exceeded your limit. << endl;


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