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Software Design Using C++

Loop Properties

The following summarizes some of the basic properties of loops in C++. This can be useful in deciding which loop to use and in avoiding problems in coding. See also the Programming Patterns section for some commonly-used patterns involving loops.
  • Number of times to do the loop body must be known in advance?
    • WHILE loop: no
    • DO..WHILE loop: no
    • FOR loop: no
      A FOR loop in C++ can do anything the WHILE loop can; it is very general. However, the answer is yes for a straightforward counting loop. Here is an example of how such a counting loop might be set up. Note that the Count must be known ahead of time:
      for (k = 0; k < Count; k++)
         cout << k << endl;
  • Minimum number of times that the loop body is executed:
    • WHILE loop: 0
    • DO..WHILE loop: 1
      This is because the condition is tested at the bottom of the loop.
    • FOR loop: 0
  • Can give an infinite loop?
    • WHILE loop: yes
    • DO..WHILE loop: yes
    • FOR loop: yes
      However, if set up correctly as a straightforward counting loop the answer is no. See above for an example of such a counting loop. (Note that it is important that the loop body does not modify k, the loop control variable. For example, if we changed this example so that the loop body decremented k by 1, using a statement such as k--, then overall the value of k would not change and we would have an infinite loop. In effect, the k-- and the k++ would cancel each other out.

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Author: Br. David Carlson with contributions by Br. Isidore Minerd
Last updated: August 27, 2009