Waznop / Lab-6---Study-For-A-While

Lab 6: Study For A While

In this lab, you will learn how to:

• use for loops
• use while loops

Question 1: for.cpp and while.cpp

For this question / while you're on this question, practice writing a program that does the same thing using a for loop and a while loop.

Program requirements

Your goal is to write a program that prints out all the multiples of 3 between 1 and 100, one number on each line.

In while.cpp, write a while loop that does this.

Then, in for.cpp, write a for loop that does this.

Note: You may only print things when inside of a loop. If you submit an assignment that does not contain a loop, or prints things outside of a loop, you will lose any points the autograder gives you.

Expected output

Your program should print one number (and nothing else) on its own line. The first few lines of the output when running the code should look like:

$ ./a.out
3
6
9
12
15
18

Question 2: prime.cpp

For this question / while you're on this question, write a program to check whether a number is prime.

Prime numbers

A number is prime if it has exactly two different factors. In other words, a number is prime if it is only divisible by 1 and itself.

If n is a number bigger than 2, n is prime if it is not divisible by any of the numbers starting from 2 up to (and including) n - 1.

Examples:

• 1 is not a prime number because it is only divisible by 1, so it only has one factor.
• 2 is a prime number because it is divisible by 1 and 2
• 3 is a prime number because it is divisible by 1 and 3 but not 2.
• 4 is not a prime number because it is divisible by 1, 2, and 4.

Program requirements

prime.cpp has some starter code that waits for the user to enter a number and stores the input in the variable n.

Edit prime.cpp to add code that does the following:

• If n is equal to or less than 0: print "invalid" followed by a newline then return 1.
• Determine whether n is prime. Hints:
  • You might need a special case for the number 1
  • Read the section on prime numbers carefully and use a loop in your code to check if n is divisible by any of the numbers between 2 and n - 1.
• If n is prime: print "prime" followed by a newline
• If n is not prime: print "not prime" followed by a newline
• Your code should not print anything else.

Example expected output

Input: 1

$ ./a.out
1
not prime
$

Input: 7

$ ./a.out
7
prime
$

Input: 12

$ ./a.out
12
not prime
$

Input: 0

$ ./a.out
0
invalid
$

(The exit code should be 1)

Question 3: pyramid.cpp

For this question / while you're on this question, practice using nested loops.

Program requirements

pyramid.cpp has some starter code that waits for the user to enter a number and stores the input in the variable n.

Edit pyramid.cpp so that it prints out a pyramid made of numbers.

• If n is negative, print "invalid" followed by a newline, then return 1.
• Otherwise, the number of layers in the pyramid should be n.
• The topmost layer should be "1". The second layer should be "121". The third layer should be "12321". And so on.
• Look at the example expected output for clarification.

Example expected output

Input: 1

$ ./a.out
1
1
$

Input: 4

$ ./a.out
4
1
121
12321
1234321
$

Input: 11

$ ./a.out
11
1
121
12321
1234321
123454321
12345654321
1234567654321
123456787654321
12345678987654321
12345678910987654321
123456789101110987654321
$

Input: 0

$ ./a.out
0
$

(Nothing should be printed if the input is 0.)

Input: -1

$ ./a.out
-1
invalid
$

(The exit code should be 1)

Hints

Break the problem down into smaller problems:

First, forget about the pyramid. Write a loop where if you have a variable i, it prints out numbers from 1 to i on one line. In other words, if i is 1, it would print "1". If i is 5, it would print "12345".

Then, write another loop where given the same variable i, it prints out numbers from i-1 back to 1 on one line. In other words, if i is 5, it would print "4321".

If you did that successfully, then you should be able to put both together and print any single row of the pyramid.

Now, write a larger loop that contains the first two loops to print all the rows from 1 to n.

Rubric

• (60 points) Programming
  • (10 points each) while.cpp and for.cpp
    • (1 point) Code compiles
    • (1 point) TODO comment check
    • (3 points) Autograder style check
    • (5 points) Autograder test case - reminder: you must use the right kind of loop in each file
  • (20 points each) prime.cpp and pyramid.cpp
    • (1 point) Code compiles
    • (1 point) TODO comment check
    • (3 points) Style check
    • (15 points) Autograder test cases
• (40 points) Written assignment – see Gradescope for point breakdowns

Due Date

• Section A: October 5, 11:59pm
• Section B: October 7, 11:59pm

See bit.ly/hwei-cs120-info for all due dates.