CSPP 50101 - Lab 1

Note that you can have multiple terminals open that the same time.

Now try your first command: Type date at the prompt and hit the enter key. This will run a program that displays the current date:

   $ date
   Mon Jun 20 09:20:30 CST 2011

   $ man date

The file system

  $ mkdir cspp50101

Use the command cd to change your current working directory to the new directory you just created (cd stands for change directory):

  $ cd cspp50101
  $ pwd
  /home/username/cspp50101

Next create a subdirectory for your work in Lab 1:

  $ mkdir lab1
  $ cd lab1
  $ pwd
  /home/username/cspp50101/lab1

  $ cd ..
  $ pwd
  /home/username/cspp50101
  $ cd lab1
  $ pwd
  /home/username/cspp50101/lab1

A first C program

Scope and Local Variables

/* returns the square of n */
int square( int n )
{
  return n * n;
}

/* displays the square of n */
void show_square( int x )
{
   printf ("show_square:  Initial value of x:  %d\n",x);
   x = square(x);
   printf ("show_square:  After x=x*x:  %d\n",x);

   return;
}

int main ()
{
   int x = 13;

   show_square(x);

   printf("\n");
   printf("main: Value of x is now %d\n", x);

   return 0;
}

  x = square(x);

  printf("main: Value of x is now %d\n", x);

Part 3 - Exercises

Exercise 1: Remote access

Use ssh to access one of these machines.

In this program, we use the conversion specifier "%.2f" with printf() to print floating point variables to the terminal:

   printf("%.2f USD = %.2f JPY \n", usd, jpy); 

Try compiling this program. You will see these error messages:

$ gcc -Wall -o ex2 ex2.c 
ex2.c: In function 'convert':
ex2.c:11: error: 'value' undeclared (first use in this function)
ex2.c:11: error: (Each undeclared identifier is reported only once
ex2.c:11: error: for each function it appears in.)
ex2.c:12: warning: control reaches end of non-void function
ex2.c: In function 'main':
ex2.c:18: error: 'jpy' undeclared (first use in this function)
ex2.c:18: error: too few arguments to function 'convert'
ex2.c:22: error: expected ';' before 'return'
ex2.c:23: warning: control reaches end of non-void function

$ ls ex2
ls: cannot access ex2: No such file or directory

ex2.c: In function 'convert':
ex2.c:11: error: 'value' undeclared (first use in this function)
ex2.c:11: error: (Each undeclared identifier is reported only once
ex2.c:11: error: for each function it appears in.)

Now look at the description of this error message:

ex2.c:11: error: 'value' undeclared (first use in this function)

There are four compile-time errors in this program (including the error on line 11). Use gcc to find and correct these errors.

Hints:

• Sometimes the actual change you need to make occurs before the line where the compiler reports an error.
• Resolve compiler errors from first to last, in the order that they appear in your code. Sometimes fixing an error on one line also fixes errors on subsequent lines.

If you use an exchange rate of 1 USD = 80 JPY then your fixed program should have this output:

$ ./ex3
199.95 USD = 15996.00 JPY

Exercise 3: Updating a program

$ cp ex2.c ex3.c

Compile and test your changes. Your output should look like this:

$ ./ex3
199.95 USD = 15996.00 JPY
199.95 USD = 139.96 EUR

Part 4 - Submitting your assignment

First, be sure that every source file that you submit includes this information in comments at the top of the file:

• Your first and last name
• Your username
• Any other comments you want to add about your program (optional)

  /* Sonjia Waxmonsky
   * wax
   * 
   * ex2.c: Converts from USD to JPY
   * 
   * Uses exchange rates from June 22, 2011
   *
   */

You will submit these files to the TA:

• A simple README file, which includes your name, username, and your list of hostnames for Exercise 1. You can also include any other comments about your work in the README. Use vi to make this README.
• File ex2.c for Exercise 2.
• File ex3.c for Exercise 3.

You should submit these files as a single .zip or .tar file. To create a zip file for this lab:

 
  $ zip username_lab1.zip README ex2.c ex3.c 

Finally, email your zip file to the Lab TA, wax@cs.uchicago.edu. You can do this quickly with the mutt command:

  mutt -a username_lab1.zip -s "CSPP50101 Lab 1" wax < "."