R – while loop
While loop in R is used when the exact number of iterations of loop is not known beforehand. It executes the same code again and again until a stop condition is met.
while loop checks for the condition to be true or false n+1 times rather than n times. This is because while loop checks for the condition before entering the body of the loop.
Syntax:
while (test_expression) { statement update_expression }
How does a While loop execute?
- Control falls into the while loop.
- The flow jumps to Condition
- Condition is tested.
- If Condition yields true, the flow goes into the Body.
- If Condition yields false, the flow goes outside the loop
- The statements inside the body of the loop get executed.
- Updation takes place.
- Control flows back to Step 2.
- The while loop has ended and the flow has gone outside.
Important Points about while loop:
- It seems to be that while loop will run forever but it is not true, condition is provided to stop it.
- When the condition is tested and the result is false then loop is terminated.
- And when the tested result is True, then loop will continue its execution.
Flowchart:
Example 1:
# R program to illustrate while loop result < - c( "Hello World" ) i < - 1 # test expression while (i < 6 ) { print (result) # update expression i = i + 1 } |
Output:
[1] "Hello World" [1] "Hello World" [1] "Hello World" [1] "Hello World" [1] "Hello World"
Example 2:
# R program to illustrate while loop result < - 1 i < - 1 # test expression while (i < 6 ) { print (result) # update expression i = i + 1 result = result + 1 } |
Output:
[1] 1 [1] 2 [1] 3 [1] 4 [1] 5
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