Can you convert a for loop to a while loop list the advantages of using for loops

Overview

This article explores some of the basic functions and uses of For Loops and While Loops in LabVIEW and the appropriate times to use them. Tutorials for both the For Loop and While Loop structures are available if you are a beginner programmer or someone looking for more instruction on configuring these loops.

A While Loop is a structure you use to execute a block of LabVIEW code repeatedly until a given condition is met. When the VI runs, the code inside the While Loop executes, and then the terminal condition is evaluated. The While Loop will be a familiar concept for experienced programmers as it operates similarly in other computer languages.

LabVIEW While Loop flowchart

Unlike a For Loop, While Loop execution does not depend on iteration count; thus, a While Loop executes indefinitely if the condition never occurs.

For more information on what a While Loop is, including its components and configuration options, look into While Loops in LabVIEW Help.

A For Loop is a structure you use to execute a block of code a set number of times. When the VI runs, the iteration count is evaluated, and then the code is executed.

LabVIEW For Loop flowchart

A For Loop can be configured to conditionally stop code execution in addition to its iteration-based exit. In these cases, the code will execute until the count terminal setting is reached or the condition is met – whichever happens first.

While Loops should be used when:

• You want your code to run indefinitely
• You want to run code until a condition is met
• You want user control over when code should stop
   

For Loops should be used when:

• You need to run code for a certain number of times
• You want to write a set number of measurements to a file
• You want to take a certain number of data points
• You want to run code until a condition is met OR a set number of iterations, whichever comes first

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The while loop is used to repeat a section of code an unknown number of times until a specific condition is met. For example, say we want to know how many times a given number can be divided by 2 before it is less than or equal to 1. If we know a specific number, such as 32, we can say 5 times, but for a given symbolic variable "NUMBER" which represents any number in the world, how many times is not known a priori (before hand). In this case, we could use a while loop to determine that answer:

The "pseudocode" for such an algorithm is: while the number is bigger than one keep dividing it by two. additionally, keep a count of how many times we do the division.

Pseudocode

            
                get our number
                set our initial count to 0
                while our number is greater than 1
                  divide the number by 2
                  increase our count by 1
                end
            
          

Matlab

            
                count = 0;
                while (number > 1)
                  number = number / 2; %  must "move" toward end of loop
                  count  = count + 1; 
                end
            
          

C, C++, or Java

            
                int count = 0;
                while (number > 1)
                {
                  number = number / 2;
                  count++; // the same as count = count + 1;
                }
            
          

Actionscript

            
                var count:int = 0;
                while (number > 1)
                {
                  number = number / 2;
                  count++; // the same as count = count + 1;
                }
            
          

Why While Loops?

1. Like all loops, "while loops" execute blocks of code over and over again.

2. The advantage to a while loop is that it will go (repeat) as often as necessary to accomplish its goal.

3. Generic Syntax:

               
     while ( condition is true )
       do something
       % Note: the "something" should eventually result
       % in the condition being false
     end
               
             

4. Infinite loops:

   If the action inside the loop does not modify the variables being tested in the loops condition, the loop will "run" forever. For example:

               
     while ( y < 10 )
       x = x + 1;
     end
               
             

               
     while (  true )
       printf('hello');
     end
               
             

Example 1: How to assure proper input

1. Ask the user to input a value.
2. while the input is incorrect.
3. ask the user to input another value.
4. go back to line 2 (the while)

Matlab

            
% MATLAB
%
% Using a while loop to ask the user to input a number
% between 1 and 10 (inclusive).
%
%   Variables:
%        value  : variable to store the input 
%

value = input ('Please Enter a Number between 1 and 10 (1-10)');

while ( value < 1 || value > 10)

  fprintf('Incorrect input, please try again.\n');
  value = input ('Enter a Number between 1 and 10 (1-10)');

end % while
            
          

C

            
/*
 * C
 * Using a while loop to ask the user to input a number
 * between 1 and 10 (inclusive).
 *
 *   Variables:
 *        value  : variable to store the input 
 */
printf("Please Enter a Number between 1 and 10 (1-10): ");
scanf("%d", &value);

while ( value < 1 || value > 10)
  {

    printf("Incorrect input, please try again.\n");
    printf("Enter a Number between 1 and 10 (1-10): ");
    scanf("%d", &value);

  }

            
          

Design Pattern:

A design pattern is the syntax that you have to memorize in order to do well in programming and on tests.

The design pattern for a while loop is:

Matlab

            
            while ( some condition is true )
              % Do this code 
              % Something here should modify the condition above 
            end
            
          

C, Java, or Actionscript

            
          while ( some condition is true )
            {
              // Do this code 
              // Something here should modify the condition above 
            }
            
          

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