At the end of this topic,
you will able to:
Explain the looping
concept.
Discuss the different
types of loops.
Explain the concepts of
event and counter controlled loops.
Write a program using
loops.
Explain the break and
continue statement in loops.
Loops
A loop is a programming
structure that allows an action to repeat until the program meets a given
condition.
After each
iteration of a loop, the loop checks against a loop control expression to see
if the program meets the given condition. If the given condition is met with,
then the loop moves to the next iteration. If not, the loop stops.
In simple words, loops
allow the program to repeat a section of code any number of times until the
condition occurs.
Types of Loops
‘C’ program, supports
two categories of loops based on where the program tests the condition:
Pre-test Loop
With each iteration, the
program tests the condition first before executing the loop’s block.
If the condition is
true, the loop continues and executes the block; if the condition is false, the
loop terminates.
With a pre-test loop,
there is a chance that, the loop may not execute.
Operation
When the test takes
place at the top of the loop, it is said to be a pre-test loop.
In each
iteration of the pre-test, the condition is tested first.
Loop Initialization
Program typically
requires some type of preparation before executing loops.
Loop initialization,
which happens before a loops first iteration, is a way to prepare the loop. It
may be explicit or implicit.
In explicit
initialization, we write codes to set the values of key variables used by the
loop.
Implicit initialization
relies on a “pre-existing situation to control the loop”.
Updating a Loop
A loop update is what
happens inside a loops block that eventually causes the loop to satisfy the
condition, thus ending the loop.
Updating, happens during
each loop iteration.
Without a loop update,
the loop would become an infinite loop.
Initializing and Updating
Here, the condition is
tested first, and then the action takes place.
After the action the
loop iteration is updated.
Event Controlled Loops
In an event-controlled
loop, an event is something that happens in the loops execution block that
changes the loops control expression from true to false.
The program can update
the loop control expression explicitly or implicitly.
We cannot predict the
number of iterations during the run of a program.
In an event-controlled
loop pre-test loop, the condition is tested first.
If the condition is
true, then the action and iterations takes place.
If the condition is
false, the loop terminates.
Counter-controlled Loops
In a counter-controlled
loop, the number of loop iterations can be controlled.
In such a loop, we use a
counter, which we must initialize, update and test.
The number the loop
assigned to the counter does not need to be a constant value.
To update, we can
increment or decrements the counter.
In counter-controlled
pre-test loop, the counter is initialized, updated and tested.
The value given in the
counter need not be of a constant value.
The number of iterations
can be controlled here.
