BIF 101 Lab 9 – if and while statements (ch 6)
Assigned: November 13, 2008
Due: November 20, 2008
For each of the following write (1) an algorithm and (2) a program to solve the given
problem. Test your program, demonstrating that it works and also demonstrating where (if
this is the case) and how it will fail (e.g. inputs are not what is expected). Paste your code
and the results of testing and results into a word file that you will submit via email.
1. avg1.pl
Input the number of test scores a user will type, and input that many scores, computing and
printing the average of the scores. Test the program with at least 5 scores and without
entering any scores. Describe what happens.
2. avg2.pl
Like avg1.pl but instead of having the user input the number of scores in advance tell the
user what to type when he/she is ready to quit (“sentinel value”). This program should also
check to see if there are no scores and should output a message – this will prevent a division
by 0 error.
3. fact.pl
Write a perl program that uses a while loop that inputs a value and computes and prints the
factorial of that value. Note that 0! is defined to be 1 as is 1! The factorial is the product of
the numbers from 1 up to a given positive integer. Make sure to test you program on a
negative number input, 0 input, and positive number input. Try typing a large positive
number – what happens? Note you may have to kill the running program with control-C.
4. fact2.pl
Like fact.pl but your program should check to make sure the number entered is > = 0 and <
= 7. The program should keep prompting the user until an appropriate value is entered.
Then the program should compute and print the factorial value.
5. loopy.pl
Choose one of the programs you have written with a loop and comment out a statement that
may cause the program to have an infinite loop. Run the program, explain what happens
and why the loop will never stop.
6. CGrich.pl
Create a program that implements the search for CG-rich regions in a DNA sequence
described in section 6.8.2 of the book. Explain how the program works.
