Problem 4

Square

Print a hollow square of hash marks, validating a size between 2 and 8.

Background

In Mario (less comfortable), you built a half-pyramid out of hash (#) characters. In this problem, you’ll build a square instead, but a hollow one: hashes around the edge, spaces in the middle.

Size (2-8): Character:

This shows what your program’s output should look like for any size and character; it doesn’t validate input the way your program needs to.

Learning Objectives

Repetition with loops
Input validation
Boolean expressions and conditionals
print() with and without a trailing newline
A function beyond main()

Specification

Implement a program, square.py, that builds a hollow square of hash characters.

Prompt the user to enter a square size.
Validate that the size is an integer between 2 and 8, inclusive. If the user enters something that isn’t an integer, or an integer outside that range, don’t print an error message: just prompt again.
Once you have a valid size, print a hollow square of that size using hash (#) characters: hashes along the top row, the bottom row, the first column, and the last column, with spaces everywhere else in between.

For example, a size of 3 should print:

###
# #
###

And a size of 4 should print:

####
#  #
#  #
####

To Get Full Credit

It’s more important that you submit a working solution than that you do everything below. Submit early, then keep improving and resubmit as many times as you like.

Structure your program with at least one function besides main(). You might write one to build the square, or one to prompt for and validate the size; that part’s up to you.
At the end of the program, add a comment describing any challenges you ran into or what you’d improve if you did this again. A sentence or two is fine.

Usage

Your program should behave like the demo below.

$ python square.py
Size: 0
Size: -1
Size: 9
Size: 2
##
##

$ python square.py
Size: 4
####
#  #
#  #
####

Bonus

For extra credit: if you run your program with a single command-line argument that’s exactly one character, use that character instead of # when printing the square.

$ python square.py x
Size: 3
xxx
x x
xxx

Your program should still work fine with zero arguments; check50 needs that to still pass.

Getting Started

Log into cs50.dev, click on your terminal window, and run:

cd
mkdir square
cd square
code square.py

That creates a new folder called square, moves into it, and opens a new, empty file called square.py for you to edit.

Style and Submission

Run these one at a time, from inside your square folder.

Check your style:

style50 square.py

Check your correctness:

check50 porttack/cs50/problems/py/square

Submit your work:

submit50 porttack/cs50/problems/py/square

Glossary

algorithm — A finite sequence of steps that solves a problem or completes a task. Can be written in English, pseudocode, or code.
loop — A statement that runs one or more statements, often repeatedly. (AP calls this iteration.)
conditional statement — A statement that controls the flow of execution depending on some condition. Informally, this is usually an if statement, which might include an elif and an else. (AP calls this selection.)
boolean expression — An expression whose value is either True or False.