Basic While Loops

Objectives

1. Understand the syntax and semantics and style of the basic while loop.

Notes

• Reference: Parts of Chapter 3, Programming in the Small II, Control.
  • We have done 3.2 Algorithm Development already.
  • We will return to chapter 2 for one section, relation operators.
  • We will only look at the while loop for now.
    • We will skip the do-while and the for loop.
    • But we will be back for them soon.
    • We will skip if statements for now too.
• We have already said that one of the strengths of a computer is the ability to repeat instructions.
• And make simple decisions.
• We will combine these into the while loop.
• The while loop

  • while (boolean-expression) 
        statement;

  • Semantics:
    1. Evaluate the boolean expression,
    2. if it is true execute the body and go to step 1,
    3. if it is false, exit the loop.
  • Look at The picture in 3.1.3.
  • Style:
    • Put the body in {}
    • Indent the body 4 or so spaces.
    • No return, break, continue, statements
• Some examples:
  • A simple loop to count up

    class looping {
        public static void main(String[] args) {
           int i = 0;
           
           while (i < 4) {
               System.out.printf("i = %d\n",i);
               i = i + 1;
           }
        }
    } 

  • In this case, i is called the loop control variable.
• Please note, in the future I will start providing code segments.
  • We should have the syntax for a main program down at this point.
  • We really don't need to look at it over and over again.
  • And I expect that our programs will be getting larger.
  • So we will only LOOK at the parts of code that are dfferent/new.
  • BUT THE REST OF THE PROGRAM is still important and needs to be included in homework and programs.
  • But if you are asked for a code segment, code snippet or something similar I want this.
  • Provide a code segment that counts from 0 to 3

  •        int i = 0;
           
           while (i < 4) {
               System.out.printf("i = %d\n",i);
               i = i + 1;
           }