195: Mainline

Now you can define the power_of_2 function using a for loop instead of a while loop. The initialization expression, counter = n, assigns the value of the parameter n to counter. Then, as long as the value of counter is not 0, the value of result, whose initial value is 1, is multiplied by 2 and the value of counter is decremented by 1.

int power_of_2 (int n) { 
  int counter, result = 1; 
  for (counter = n; counter; counter = counter - 1) 
    result = 2 * result; 
  return result; 
} 

Augmented assignment operators reassign a variable to a value that your program obtains by combining the variable's current value with an expression's value via addition, subtraction, multiplication, or division. The following diagram illustrates how assignment using an augmented assignment operator differs from ordinary assignment:

variable name = variable name operator expression 
                                   | 
                                   | 
                                   | 
                 *-----------------* 
                 v 
variable name operator= expression 

For example, you can rewrite result = result * 2 in this way:

result *= 2 

Even though this shorthand gives you a perfectly valid way to multiply and reassign, you may choose to write result = result * 2, which you see throughout this book, on the ground that result = result * 2 stands out more clearly as a reassignment operation.