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CS439: Principles of Computer Systems

Homework 1, Part 1

Due: 8:45a Friday, January 30, 2015

Part 1 of the homeworks must be submitted electronically. Please refer to the homework turnin instructions.

  1. Create a name tent for use during all discussion sections this semester. Your name tent should be typed. If you are unsure of either what a name tent is or how to create one, many examples can be found using Google (probably the one and only time this semester we will recommend Google). Bring your name tent with you to discussion section.
  2. Describe what a pair programming log in this course should contain. How often should the pair/group change drivers? How much time must the pair/group spend programming together?
  3. Run the following command in your command line (it generates 10k random integers less than 100 and stores them in the num.txt file.):
    $ for i in {1..10000}; do echo $(($RANDOM % 100)); done > nums.txt
    
    How many 12 are in num.txt? How many 10? How many 87?
    What command did you use to answer this question?

    Hint: You don't even need to open the file to answer this question. You may find grep and wc useful.

  4. Note that problems 3-6 are related.
    Write a C program that expects an integer command line argument, x, and then uses recursion to print, Hello, World! x times. Paste the code into your homework.
  5. Compile your program from 3) on the CS Linux machines using gcc. Use command line options to:
    1. Name the executable file hello.
    2. Set the optimization to level 0.
    3. Turn on the debugging information.

    You may find the overview of gcc on the course homepage helpful.

  6. Run your program from within gdb with an argument of 5.
    1. Set a break point at the entrance to your recursive function.
    2. Print the value of the argument to the function.
    3. Step through each line of the function until Hello, World! is printed.
    4. Continue the execution until the next breakpoint is reached. Check the value of the argument, and, if it is not the last recursive call, continue the program.
    5. On the last recursive call, print a backtrace of the call stack. Identify the line number of the call to your recursive function in main().

    What commands did you use in gdb? What is the line number of your recursive call?

  7. Return to your program and add an if statement in main after the recursive call that reads:
    if(x == x)
       printf("Goodbye\n");
    
    where x is the name of the argument to the recursive call. (If you didn't save it into a variable before, please do so now!)

    Recompile your program with the optimizations set to level 4.

    Run your program using gdb, but set a breakpoint in main for the if statement and inspect the value of x. What do you learn?