Chapter 4.5, Problem 18CP

Explanation of Solution

Sentinel:

Sentinel is the special value which is used to stop the sequence of series when there is no indication of explicit size.

• • It is also called as “flag value” or “dummy value” created in the algorithm to terminate the program.
• • The sentinel value must be a distinct value from the other data values, so that it is guaranteed to end the data.
  • ○ For example: “null character” is used to end the null terminated string and a “negative integer” is used to indicate the end of sequence for non-negative integers.
• • Whenever the program reads the sentinel value it stops the execution of loop, because it knows that it reaches the end of sequence.

Example program:

The following program code uses the sentinel value:

#Initialize the variables

total = 0

counter = 0

# Get the marks

Marks = int( input("Enter marks, -1 to end: "))

'''Check loop if marks not equal to -1 sentinel value to terminate the loop'''

while Marks != -1:

         # Calculate the total

         total = total + Marks

         # Increment the counter by 1

         counter = counter + 1

 ...