Question

Explain the similarities and differences of counter-controlled iteration and sentinel-controlled iteration. Also, give an example of how each would be used in a computer program.

Answer 1

Iterative:

The iterative statement like for() loop, while() loop, do-while() loop, etc uses the iterative statement and allows the set of instructions to be repeatedly executed. These statement includes initialization, condition, and update the control variable and repeatedly executed until a certain condition is reached.

Counter controlled iteration:

The counter controlled loops are executed for a specific number of times.

For example:

for() loop

The syntax for the 'for' loop is given below:

for(expression1, expression2, expression3)

{

//statement

}

The expression1 is executed only once and before the loop body execution.

The expression2 define a condition for the body of the loop

The expression3 is executed every time at the last of the loop body.

For example:

for(int i=0; i<10; i++)

{

//statements

}

The above 'for()' loop will execute for 10 times.

This loop should be used when we know the number of iteration in advance.

Sentinel controlled iteration:

Sentinel value is a special value that is used to terminate a condition in a loop or recursive execution.

For example:

For example:

while(condition)

{

//statements

}

The while loop will be executed until the condition is true and will exit when the condition will be false.

Difference:

• The sentinel-controlled iteration can be used when we don't know the number of iteration in advance. Counter-controlled iteration can be used when we know the number of iteration in advance.

• In sentinel-controlled iteration, the controlled variable is known as the sentinel variable but in the counter-controlled iteration, the controlled variable is known as a counter.

• The example of sentinel-controlled iteration is while() and do-while() loops but the example of counter-controlled iteration is for() loop.

Similarities:

• Both of the iterations are used to execute a group of statements or a single statement for a number of times.

• Both of the iterations define an exit condition to avoid the infinite iteration.