1. ENEE150 Discussion 04
Section 0101
Adam Wang

2. Overview
HW2
Pointers

3. HW 2 Problem 1
Write your own “tests” to test the check functions in project 1
Check_basic_move
Check_entry_move
Check_bear_off_move
Check_die
Check_board_bounds
You’ll submit 5 programs: test1-driver.c -> test5-driver.c
Just print out whatever’s in the out files

4. What you’re given required_functions.o Test1.out -> test5.out
Contains the 5 check functions and print_board()
A *.o file is compiled but not linked; you can use it but you won’t be able to see the code
Use like you would use a *.c file
Test1.out -> test5.out
All the output you need to be able to print with the driver programs
Copy in your backgammon.h for the function headers and global variables

5. Test1.out Put 1 white piece on the_board_white[6]
You’ll first need to clear the board
Go through the_board[] and set everything to 0
Put 1 white piece on the_board_white[6]
Print_board
Use simple if statements to decide if you should print “VALID_MOVE” or “INVALID_MOVE”
Next put 1 red piece on the_board_red[1]
Print board again
Do same thing over again

6. Problem 2: run-tests
Write a script file to automatically compile & diff all your files
This is NOT a *.c file; this is a shell language
Should be ~10 lines of commands

7. Tips to write the script
First line must be #!/bin/csh
This tells the shell it’s a cshell script
The command to print is echo
echo “hello world”
A “for” loop looks like this:
foreach i ( )
...
other commands go here (gcc, diff, a.out, etc.)
end

8. Other tips In a for loop you can use the value of i in your commands
test$i-driver.c
Replaces “$i” with whatever value i is
After you’ve written and saved, you need to change permissions
Type “chmod 777 run-tests” to give yourself executable permissions
Then you can run the script just by typing run-tests

9. Pointers Stores a memory address in hex
Can also say it’s a “reference” to another variable or value
To initialize a pointer: int *p;
Right now this memory address points to garbage
& - get the memory address of a variable &a
* - get the value at the pointer *p
Also “dereference” a pointer

10. Examples int *p; // new pointer p int *q; int a, b, x; a = 5;
*p = a; // set the value of p to whatever’s a
b = 6;
q = &b; // set q to the memory address of b
b = 7; // what happens?
q = p; // valid
x = *p + 5;

11. Where have we seen pointers already
FILE * inFile;
inFile = fopen(“data.txt”, “r”);
Stores a pointer to a FILE data type
Scanf(“%d”, &var);
Reads in an integer and stores it into var
Why do we need to do this?

12. swap
void swap (int a, int b) { int temp = a; a = b; b = temp; } int a = 5, b = 10; swap (a,b); // Does NOT work; pass by VALUE

13. Let’s consider this new swap function
void swap (int *a, int *b) { int temp = *a; *a = *b; *b = temp; } int p, q; p = 5; q = 10; swap (&p, &q); //This works because of pass by REFERENCE