CS31 Lab 1: C Programming Basics

When run, your program’s output should look like the example output shown in Section 4.1.

You should implement at least the three required functions, including adding their function prototypes to the top of the prog.c file and their implementations at the bottom (like read_int).

You should only use parts of the C programming language that we have covered in class to solve this lab. Specifically, if you have taken CS35 (or have prior experience in C or C++), and if you are familiar with C string, array, or pointer variables, you may NOT use any of these in your solution.

Your picture drawing must use nested for loops, and must be done by making calls to print a single space, a single star, or a single new line:

printf(" ");
printf("*");
printf("\n");

Your code must be well-commented, modular, robust, and use meaningful variable and function names. Each function should include a brief description of its behavior, and a description of each parameter and what it returns. Also, do not wrap lines and follow C-code conventions with local variable declarations and function prototypes.

Your code should compile cleanly with no errors or warnings and should not crash unexpectedly during execution.

Code you submit should have my "TODO" comments removed (these are my notes to you, as you implement them remove the "TODO").

Any debugging output should be removed (or commented out) from your submission for grading; again, your program’s output should match Section 4.1

You should use vim editor for editing your prog.c file.

Start early on this. We strongly recommend not using any of your late days on this lab assignment.

Type CNTL-C in the terminal to kill a program stuck in an infinite loop. read_int is not super robust to bad user input, such as the user entering hello there instead of a valid int value. As a result, it could trigger an infinite loop, as could any loop code you add.

Start by implementing and testing the compute_ave function, and test for several input values to ensure correctness. To verify that your function is correct, think about what you expect the average of a set of random values in the range you pass to be. Your result should be close to this. Since the values are randomly generated, and since the program calls srand to seed the random number generator each run, two runs of your program using the exact same user input may produce slightly different average results.

The C mod operator (%) can be applied to two int operands and evaluates to the remainder part of int division. For example, num % 5 returns a result in the set [0,4] depending on the remainder of the value of num divided by 5 (10 % 5 evaluates to 0, and 102 % 5 evaluates to 2).

Think carefully about type in C, and the effects on how operators are evaluated. For example, if both operands to / are int, / does int division. If at least one is a float (or double), / does float (or double) division.

printf takes a format string that can include placeholders for argument values. %g is a placeholder for a float or double, and %d is a placeholder for an int value. Make sure that the type of the placeholder you use matches the type of the argument you pass for it. If not, your program’s output may be incorrect only because of this mismatch (i.e. you are computing the correct result, you are just printing it out incorrectly).

int get_in_range(int lo, int hi); can be used for both questions related to the picture drawing part of your program. After printing out a message with the range of value to input, it should call read_int("value: ") to get the input value entered by the user. It should not return until the user enters a valid input value (one in the specified range). Look at the example runs in Section 4.1 to get a sense of what this function does and prints out when the user enters a value not in range and it repeats reading in a value until the user does enter one in range.

For the draw_picture function, you can have more than one inner loop in the outer loop, but you do not need more than double nesting. It is worth thinking about the pattern on paper a bit before coding. Consider that the outer loop controls how many lines are printed, and the inner loop(s) what is printed each line. If what is printed each line changes (and it does), come up with a pattern for how many stars (and how many spaces) are printed based on which line is being printed (which i value for the outer loop variable).

As a first step in determining how to implement the draw_picture, you can start by solving an easier drawing problem, and then modify it bit by bit to draw more complicated patterns until you draw the mountain pattern. For example, you could start first by drawing a box of stars based on size:

value: 3
***
***
***

value: 8
********
********
********
********
********
********
********
********

value: 3
*
**
***

value: 8
*
**
***
****
*****
******
*******
********

value: 3
   *
  **
 ***

value: 8
        *
       **
      ***
     ****
    *****
   ******
  *******
 ********

Start on this early, and post on Piazza, attend ninja sessions, and/or come to office hours if you have questions!

Class piazza page for questions and answers about lab assignment

CS31 github org

Git for CS31 labs

Git help

Dive into Systems, Chapter 1 on C programming

Some Useful Unix Commands

vi (and vim) quick reference

compiling and running C programs on our system

C code style guide

make and makefiles