CS 2073, Spring 2006  Program 8  Random Walk in the Plane  Due (on time): 2006-04-07  23:59:59  Due (late):        2006-04-10  23:59:59

Program 8 must be emailed to: nrwagner@cs.utsa.edu following directions for: running and submitting a C program, with deadlines: 2006-04-07  23:59:59 (that's Friday, 7 April 2006, 11:59:59 pm) for full credit. 2006-04-10  23:59:59 (that's Monday, 10 April 2006, 11:59:59 pm) for 75% credit.

New: The web page Mulitplication Table illustrates some of the code needed for this assignment.

1. Use a 40-by-40 grid for the walk, perhaps defined by:

   char g[40][40];
   

   Normally, we would use a defined constant for the size of the grid:

   #define SIZE 40
   char g[SIZE][SIZE];
   

2. Use two variables, say x and y, to keep track of the x and y coordinates of the location of the random walk at each step. Start the walk at SIZE/2 for each coordinate, so that x and y will each be initialized to this quantity.

3. Use a loop to carry out the random walk, starting the walk out by the initialization in the previous item. At each step in the walk (that is, each time the loop is executed), use a random number to decide on the new location, which must be either one space up, one space down, one space right, or one space left. In other words, one of the new coordinates stays the same and the other changes by +1 or -1.

4. The random walk must stop when you first reach the boundary. This means that the loop in the item above must be terminated (break from the loop) in this case. This occurs when either coordinate would become equal to -1 or SIZE. If the walk actually moves to such a location, then it would reference an out-of-bounds coordinate of the grid, which is a serious mistake in C (serious because it does not cause a run-time error, as it does in Java). Instead, the walk should be terminated.

5. Initialize all chars in the grid to blanks. Use a separate function to do this, say with prototype:

   void blankgrid(char g[SIZE][SIZE]);
   

6. For each location on the random walk, overwrite that char with a *, so that the walk appears as all stars. The walk may loop back on itself, and since it is all stars, you won't be able to tell exactly how the walk goes.

7. Print the new version of the grid with the stars present. Use a separate function to do this, say with prototype:

   void printgrid(char g[SIZE][SIZE]);
   

8. Keep a count of each step of the random walk, and print the total length (number of steps) at the end.

9. Also fix it up so that the first step of the walk is printed as a '#' (easy to do), and the last step (the one just before stepping out of bounds) is printed as a '$' (a little harder). [Hint: insert these two characters into the array after all the rest are inserted. '#' can just be inserted at the center, but for '$', you have to save the old location each time so that you can use the previous location for '$'.]

10. As a final feature, fix up the print-out so that it looks like the following: Sample random walk. This should be done using the defined constant SIZE, so that changing this constant to 50, say, would still produce the enhanced boundary.

1. Create and run a C program that uses stars for the random walk. Be sure to print the number of steps. Show two runs, one with fewer than 520 steps and one with more than 520 steps.

2. Create and run a C program that uses SIZE equal to 50. Be sure to print the number of steps. Again show two runs, one with fewer than 520 steps and one with more than 520 steps.

For extra credit, enhance the program so that instead of printing all stars, it prints an 'A' 10 times, then a 'B' 10 times, ... , then a 'Z' 10 times, then an 'a' 10 times, then a 'b' 10 times, ... , then a 'z' 10 times. After 520 steps in the random walk, you should start over with 'A' again. [Hint: you can use a string defined by:

char alf[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
             "abcdefghijklmnopqrstuvwxyz";

This defines a string of length 52, so that alf[0] through alf[51] refer to characters 'A' through 'z'. Then you can take the current number of steps up to a give square, divide by 10, and remainder by 52 to get an index into the alf array.]

Contents of email submission for Program 8: Last Name, First Name; Course Number; Program Number. C source for item 1 above and two runs. C source for item 2 above and two runs. C source for the extra credit part. One run is enough.