Lab 03 Testing your assumptions solution


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Lab 03

Testing your assumptions
Very often when programming, certain assumptions are made. While this helps simplify the task at hand,
sometimes our assumptions can be wrong. For example, if you are certain that a list will never have more
than n elements, you can state this with an assertion:
assert(list_size <= n);
Now list_size will be compared with n every time the assert() call is reached.
A few important notes about using assertions:
• you must #include <assert.h
• assert()s should only be used by you (the developer) to validate your assumptions – they should not
be used for error handling
• assert()s can be disabled by adding -DNDEBUG to your compiler flags
• the golden rule of using assertions: they cannot change any state in your program (had the above
assertion used n++ instead of n the program would no longer have the same semantics)
If malloc() fails that is not recoverable so checking the value returned from malloc() is not a good candidate
for using assertions (even though we do it in the sample code). Checking that a pointer has a valid value
before you dereference it may be acceptable but only if you expect it to be valid, i.e., that is the behavior
you expect from your program.
Download assert_test.c and get it working. Don’t forget to add the -Wall option to either clang (recommended)
or gcc (OK, too).
Write a grading program that asks for a student’s grades. Use malloc() to allocate enough space for all of
them. Use this web page to only print out two digits of precision (search for precision).
How many grades does the student have? 4
Enter the next grade: 92
Enter the next grade: 98
Enter the next grade: 100
Enter the next grade: 93
The average grade is 95.75
Better Grades Program
Repeat the program above but this time create a struct student that should be defined like so:
struct student
char name[100]; // No one should have a name longer than this
int *grades; // This is the pointer to hold the (integer) grades
int count; // The number of grades
Ask how many students and allocate them. For each student, ask how many grades and allocate those as
well. Sample output below:
How many students are there? 2
Enter the name of student 0: Jenny
How many grades does Jenny have? 4
Enter the next grade: 92
Enter the next grade: 98
Enter the next grade: 100
Enter the next grade: 93
Enter the name of student 1: Bill
How many grades does Bill have? 3
Enter the next grade: 91
Enter the next grade: 88
Enter the next grade: 94
Jenny has an average grade of 95.75
Bill has an average grade of 91.00