Lab 1. Introduction to Linux and C++ Solution

Making sure that all have Gradescope invite (and resend to the ones that do not using their EMPLID and email that they actually use), and have everyone create their Gradescope account.
Review of some Unix terminal commands from CSCI127.
 
You need to know just a few commands to work comfortably in a Unix terminal:
ls, cd, pwd, mkdir, cp, mv, rm.
A brief summary:
pwd  
print the current working directory
ls  
list files in the current directory
ls path/to/a/directory  
list files in the directory
cd path/to/a/directory  
change directory
cd ..  
go to the parent directory (one level up)
mkdir newdirectoryname
create new directory
cp file1 file2  
copy file1 and call the copy file2
mv file1 file2  
rename (move) file1 to file2
rmdir directoryname  
remove empty directory
rm file  
remove file
These are some useful directory shortcuts:
.  
the current directory
..  
the parent directory of the current
~  
the home directory
And these additional unix commands:
touch newfilename  
create new file
chmod <options> file  
change file permissions (read +r, write +w, execute +x)
man command  
documentation about the command
Also read this article and watch its videos:
Become a Command Line Ninja With These Time-Saving Shortcuts
Try this Unix tutorial for more information.
Compiling C++ code with g++.
First, get acquainted with the gedit Text Editor, which you will be using to write your C++ programs.
Now, lets set the default tab width on your Text Editor to 3. Once you open it, click on Text Editor in the upper left corner of the screen and select Preferences from the drop down menu. Click the Editor tab and set Tab width to 3. Done!
Regarding coding style: remember that it is of paramount importance that all of your code is correctly indented. You must always use tabs to indent lines of code. Never use spaces to indent! In addition to automatic grading by Gradescope, we will spot check your code manually and will reduce your grade, if the indentation is not correct or if spaces are used instead of tabs.
Consider the following program that asks for your current age and prints it on the screen:
#include <iostream>
using namespace std;

int main() {
        cout << "Enter your age: " << endl;
        int age = 0;
        cin >> age;
        
        cout << "Your age is " << age << "." << endl;
}
To compile program code.cpp and call the executable myprog, type in the terminal:
g++ -o myprog code.cpp
To run the produced compiled program:
./myprog
Alternatively, if you compile the program without giving the output file name (such as -o myprog), the executable file will be called a.out, which you can execute the same way:
./a.out
How to compile and run programs on your own computer?
There are three components you should make sure you have installed:
    • g++ compiler,
    • a functioning terminal application, and
    • a good plain text editor (Gedit, Emacs, Vim, or Sublime Text) to write programs.
If your computer OS is Linux or Mac OS, you already have everything! If it is Windows, please follow this excellent tutorial: Linux on Windows Tutorial

 . OSX. You already have everything. It may come with g++ pre-installed. If you have it setup, this is all you need for most of the course.
How to submit your programs.
Each program should be submitted through Gradescope.
Write separate programs for each part of the assignment.
Submit only the source code .cpp files, not the compiled executables.
Each program should start with a comment that contains your name and a short program description, for example:
/*
Author: your name
Course: CSCI-136
Instructor: their name
Assignment: title, e.g., Lab1A

Here, briefly, at least in one or a few sentences
describe what the program does.
*/
Task A. Find the smaller of two integers.

Write a program smaller.cpp that asks the user to input two integer numbers and prints out the smaller of the two.
Example
$ ./smaller
Enter the first number: 15
Enter the second number: -24

The smaller of the two is -24
Task B. Find the smaller of three integers.

Write a program smaller3.cpp that asks the user to input three integer numbers, and prints out the smallest of the three.
(Hint: There are many possible solutions here. One possible strategy: Given numbers x, y, and z, you can first compare x and y, take whichever is smaller and compare it with z.)
Example
$ ./smaller3
Enter the first number: 23
Enter the second number: 76
Enter the third number: 37

The smaller of the three is 23
Task C. A leap year or a common year?
Introducing the modulo operator %
In C++, operator % computes the remainder of the division of x by y. For example, 37 % 10 returns 7, because this is the remainder of 37 when divided by 10.
The task
Write a program leap.cpp that asks the user to input an integer representing a year number (1999, 2016, etc.). If the input year is a leap year according to the modern Gregorian calendar, it should print Leap year, otherwise, print Common year.
In the modern Gregorian calendar, a year is a leap year if it is divisible by 4, but century years are not leap years unless they are divisible by 400. Here is the pseudocode:
if (year is not divisible by 4) then (it is a common year)
else if (year is not divisible by 100) then (it is a leap year)
else if (year is not divisible by 400) then (it is a common year)
else (it is a leap year)
This means that 2012, 2016, 2020, and 2040 are all leap years.
However, the century years 1800, 1900, 2100, 2200, 2300 and 2500 are NOT.
Yet, 2000, 2400, 2800 are still leap years.
Example 1
$ ./leap
Enter year: 2016

Leap year
Example 2
$ ./leap
Enter year: 2017

Common year
Task D. Number of days in a given month

Write a program month.cpp that asks the user to input the year and the month (1-12) and prints the number of days in that month (taking into account leap years). You may not use switch case or arrays even if you know these language constructs.
Example
$ ./month
Enter year: 2017
Enter month: 5

31 days