Looping With a Known Loop Count

Just do something 5 times.

Loops With a Known Loop Count

• A very common looping task in programming is to loop a predetermined amount of times.

• We can code this with while loops or for loops. They are all equivalent in functionality. However, programmers tend to favor the for loop for this.

• Let's look at it with the while loop first then the for.

• Here's a small program that does something exactly 5 times.

/*
    This function is in file unit04/demos/js/knownLoopCount.js.
    It loops five times with a while loop
*/
function whileFiveTimes() {
    "use strict";

    // Declare Constants
    const INITIAL_VALUE = 0;
    const LOOP_LIMIT = 5;

    // Declare Variables
    let counter;

    // Initialize the counter
    counter = INITIAL_VALUE;

    while (counter < LOOP_LIMIT) {
        document.write("This is loop number: " + counter + "<br />");
        counter++;
    }
}

• And here it is with a for loop.

/*
  This function is in file unit04/demos/js/knownLoopCount.js.
  It loops five times with a for loop
*/
function forFiveTimes() {
    "use strict";

    // Declare Constants
    const INITIAL_VALUE = 0;
    const LOOP_LIMIT = 5;

    // Declare Variables
    let counter;

    for (counter = INITIAL_VALUE; counter < LOOP_LIMIT; counter++) {
        document.write("This is loop number: " + counter + "<br />");
    }
}

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They look very similar. The main difference is that the for loop has one less line of code.

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The while loop does the same thing, only differently.

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Example: Fahrenheit-Celsius Conversion

Demo

1. Demo: Fahrenheit-Celsius Conversion
   • unit04/demos/demo-fahrenheit-celsius.html

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Not everything that can be counted counts, and not everything that counts can be counted. -Albert Einstein

Read more

Related Reading

Pages 57 - 67

Hands on Work

Labs

1. Lab05: While Loop with known Count
   • unit04/labs/lab-05-while-known-count.html
2. Lab06: For Loop with known Count
   • unit04/labs/lab-06-for-known-count.html

Exercises

1. Lab05 exercise
   • unit04/exercises/exercise-05.html
2. Lab06 exercise
   • unit04/exercises/exercise-06.html