Lab 07 - Compiling with Clang

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Lab 7 Slides

Exercise 4 Review

Dynamic Array

1. malloc() - memory allocation

2. calloc(n, m) - calculate the allocation. And it means allocate a memory space for n values, each of size m.

When do should we use malloc()/ dynamic array?

When we don't know the size of the array at the time we run the program. If we know the size of array, use a static one like long a[10] is enough.

Note that calloc() will "clear the memory" with 0 before it returns the pointer back. So that is why we are recommended to use calloc()!

Null Pointer Check

If you don't do Null Pointer Check, you will be penalised in PE

7. Kendall

Use math to simplify the algorithm

For each i in permutation:
    for each j before i:
        if j > i:
            count += 1

9. Subtract

An idea to ignore the leading zero is to use start print from the first nonzero element if the result is not 0.

Compiler

1. clang -I, -I stands for "include"

Multidimensional Arrays

1. Remember the way to allocate a 2-D array (with null pointer check)

2. If the contiguous memory method, the code below

for (long i = 1; i < m; i += 1)
{
    matrix[i] = matrix[i - 1] + n;
}

This will define the starting point for each row.

1. Due to array decay, the address of an array is the same as the address of its first element.

Big O

1. $f(x) = O(g(x))$ means f(x) is upper bounded by g(x). or $f \in O(g)$, which means set of all functions which do not grow more slowly than f.

2. Include the trivial results about Big O calculation in the cheatsheet.

3. If you have two inputs m and n, you should include both variables because they are independent.

4. The real way to compare growth rate is to take the limit.

Selected Problems from Exercise 5