Difference between “while” loop and “do while” loop

Question

What is the difference between while loop and do while loop. I used to think both are completely same.Then I came across following piece of code:

do {
                


        

Answer 1

While Loop:

while(test-condition)
{
      statements;
      increment/decrement;
}

1. Lower Execution Time and Speed
2. Entry Conditioned Loop
3. No fixed number of iterations

Do While Loop:

do
{
      statements;
      increment/decrement;
}while(test-condition);

1. Higher Execution Time and Speed
2. Exit Conditioned Loop
3. Minimum one number of iteration

Find out more on this topic here: Difference Between While and Do While Loop

This is valid for C programming, Java programming and other languages as well because the concepts remain the same, only the syntax changes.

Also, another small but a differentiating factor to note is that the do while loop consists of a semicolon at the end of the while condition.

Answer 2

The difference between a while constructs from Step 1 versus a do while is that any expressions within the do {} will be running at least once regardless of the condition within the while() clause.

println("\nStep 2: How to use do while loop in Scala")
var numberOfDonutsBaked = 0
do {
  numberOfDonutsBaked += 1
  println(s"Number of donuts baked = $numberOfDonutsBaked")
} while (numberOfDonutsBaked < 5)

Here is detail explaination: Explanation Visit: coderforevers

Answer 3

Do while loop will be executed atleast once.......but while loop will check the condition first and then it may or may not get executed depending on the condition.

In your example wdlen may assume any garbage value which is > 2 so while loop will never get executed.

whereas do while loop will be ececuted and will tell u to enter the value and check that value in terminating condition

Answer 4

The do while loop executes the content of the loop once before checking the condition of the while.

Whereas a while loop will check the condition first before executing the content.

In this case you are waiting for user input with scanf(), which will never execute in the while loop as wdlen is not initialized and may just contain a garbage value which may be greater than 2.