% CSC 211 Lab 2: Command-line arguments and Echo % Spring 2018
Last lab, you explored the Linux bash command-line environment. Several of the commands you used, such as cd and cp, take command-line arguments, which are very much like the arguments to a function, except they apply to the execution of a whole program. Another command that takes command-line arguments is echo, which simply repeats back all its command-line arguments, separated by spaces.
Here, you're going to write a program, not in the Mimir editor, but using your text editor (e.g. Atom) and the Docker environment.
You should do this lab with a partner. But, you will submit the lab individually.
You should know how to do this by now.
Play with the echo command a little bit. Type echo hello followed by enter. Play around with some other arguments to echo, including multiple arguments (with spaces in between) such as echo hello there.
Type git clone https://github.com/csc211/lab2 (followed by enter, of course, which you should assume by now).
You'll see some informational output. Type ls and note that you'll see a lab2 directory. Change directory into there by typing cd lab2. Type ls and see what's there. Now, go to your text editor (e.g. Atom) and open up the lab2 directory within your CSC211 directory on your desktop. Note that there are a few files in there. Two of them are these lab instructions (one as a .md file, which is a simple formatting language known as markdown, and the other as a PDF). One is called compile and it's a script that will let you compile your code. The other is an empty file called echo.cpp which you need to write.
- You need to write a
main()function. For this lab, you probably won't need any helper functions, though. - Your program must print out each of its command-line arguments, with one space in between each argument. After this, it must print a newline character.
- If your program is given no command-line arguments, it should simply print a newline character.
- This behavior is identical to the command
echoyou just tried out. You're re-implementing the Linuxechoprogram.
- You will compile your program by typing
./compile(followed by enter, of course).- This will produce an executable binary called
echo - Don't try to write the whole thing and then compile it.
- Instead, compile whenever you think the program might compile.
- This will save you a huge amount of time.
- Remember to look at the top-most compiler errors, not the bottom-most ones.
- This will produce an executable binary called
- You can then run your program by typing
./echo(followed by any arguments you wish to provide to it). - You will need the type signature for
main()that allows command-line arguments:int main(int argc, char *argv[])
- Remember that
argccontains the number of elements inargv- But also remember that
argv[0]is the name of the program, which you want to skip
- But also remember that
- You need to print out each element of
argvexcept forargv[0] - You need to print a space after each one except the last one.
- After the last one, you need to print out a newline character
- You can print out a newline character with
std::cout << endl
- You can print out a newline character with
- Given a
char *namedfred, you can print it out with:std::cout << fred- But, in order to be able to use
std::coutyou will need to put#include <iostream>at the very top ofecho.cpp
- Think about what you might need to do differently with the last entry in
argv. Remember that you are printing a space between each entry, but not after the last one. After the last one, you're printing a newline. So, think carefully about whatever programming construct you use to solve this problem.
Go to Mimir, and go into Lab 2. Create a group for you and your partner, as you will submit one solution for both of you. Then, upload your echo.cpp file to Lab 2. You don't need to upload any other files.