Observations on the for loop

• If a control variable is declared in the initialization part, then its scope is limited to the for statement. This becomes clear if we look at the equivalent while loop, in which the entire code corresponding to the for loop is enclosed inside a block.

  Example:

  for (int i = 0; i < 10; i++) {
    System.out.println(i * i);
  }
  // System.out.println("value of i = " + i);
                                    // ERROR! i is not visible
  

• Each of the three parts of the for loop (i.e., initialization, condition, and update) could also be missing. In this case, the ";" have to be inserted anyway. If condition is missing, it is assumed to be equal to true.

• The syntax of the for loop allows all three parts to be arbitrary expressions, as long as initialization; and update; are statements (in particular, they must have a side-effect).

  However, when using the for loop the following is recommended:

  • Use the three parts of the for loop according to their intended meaning described above, and with reference to a control variable for the loop;
  • Do not modify the control variable in the body of the loop.

• In general, initialization and/or update can be a sequence of expressions with side-effect, separated by ",". This would allow us to initialize and/or update more than one control variable at a time. However, it is recommended not to do so.

  Example: Calculate and print the first 10 powers of 2.

  int i, powOf2;
  
  for (i = 0, powOf2 = 1; i < 10; i++, powOf2 *= 2)
    System.out.println("2 to the " + i + " = " + powOf2);