1. CS1010 Discussion Group 11
Week 6 – One dimensional arrays

2. Slides are at http://www.comp.nus.edu.sg/~yanhwa/
HELLO!
Slides are at

3. Lab 2 Tips
Did not put repeated ordinal number lines of code in sum and average in a separate function print_ordinal
Can use round() for averaging, besides +0.5 or x10 and checking last digit
Remember to initialise variables before using it in while condition (eg. command_code)
Indentation. Use gg=G. Note indentation of break; and ifelse
Meaningful variable names. Num, sum, index, tmp, calc
Comments, last_digit = index % 10. When does while loop end? What are your assumptions for input?
Recursion, arrays not allowed
Input to be entered is from 1 to 1000, need to take care of 111, 112, 113 too
Complex logic – unnecessary cases, else if else if else if

4. Multiple ways to do lab 2

5. Moral of the story: Try not to mix I/O and calculation
Lab 2 Tips
For tasks 2 and 3, the I/O and the calculation may be mixed inside functions, which may be considered BAD function design in CS1010. But since currently we haven't taught arrays, this can be tolerated in lab2.
Moral of the story: Try not to mix I/O and calculation

6. signal = parse_command(); } while (signal != -1);
Lab 2 answer
in main()….
int signal = 1;
do {
signal = parse_command();
} while (signal != -1);
Thus if (command_code == COMMAND_EXIT) will eventually return -1 in parse_command(). Everything else will return 0 in parse_command(). Parse_command() uses a while(1) loop but the return statement will exit out of the entire function.
Use do_while(command_code != COMMAND_EXIT), or use a similar while loop. Note that using a while loop, you need to initialize the value of command_code, but for do_while it is unnecessary.

7. Lab
CodeCrunch Lab #3
Have you submitted?

8. PE on Friday! Lab Check your session. Session 2?
This is an open-book test. You may bring in any printed or written material. 
The scope of PE1 includes everything that is covered up to and including Repetition Statements. 
You are not allowed to use recursion, arrays or string functions from string.h.
See marking scheme, PC number, plab account, computer lab number

9. #Lab 2 Do
Split similar code into functions so that you Don’t Repeat Yourself
Initialise when necessary
Have clear logic
Add comments at important, not trivial areas of code
Must do
Double/triple check your indentation (gg=G in vim will auto-indent your program nicely!)
Add function description, preconditions and postconditions (if any)
Do not
Add function description elsewhere other than on the top of the function
Use arrays or recursion in the labs for now
Follow lab guidelines

10. THE ARRAY data structure
Lecture Summary
int c[10];
a[0]
a[1]
a[2]
a[3]
a[4]
a[5]
a[6]
a[7]
a[8]
a[9]
A series of “containers” that stores data of the same type
Has a name and is allocated memory. “name” points to address of first container
Each container has an index (starting index is 0 or 1)
Has a fixed size (?) Variable-length arrays not supported by ANSI C90.
Can be initialised at time of declaration
int cand[NUM_CANDIDATES] = { 0 };
#define M 5
#define N 10
double foo[M*N+8]; // size of foo is 58

11. Do you know how to… int sumArray(int arr[], int size) { ... }
Lecture Summary
Do you know how to…
Declare and initialise array
Access array elements using index
Copy array data into another array
Create a function with array as parameter arr[]
Pass an array to a function as an argument
When an array is passed to a function, a pointer to the address of first element of the array is copied into the function. NOT THE ARRAY DATA
Write I/O functions for array
int sumArray(int arr[], int size) { ... }

12. while ( condition ) { // loop body }
Do you know how do_while works? What if n is negative?
Lecture Summary
// Precond: n > 0
int add_digits(int n) {
int sum = 0;
return sum; }
while ( condition ) {
// loop body }
do {
sum = sum + n%10;
n = n/10;
} while (n > 0);

13. Will this work? double one_seventh = 1.0/7.0; double f = 0.0; do {
Lecture Summary
double one_seventh = 1.0/7.0;
double f = 0.0;
while (f != 1.0) {
printf("%f\n", f);
f += one_seventh; }
do {
sum = sum + n%10;
n = n/10;
} while (n > 0);

14. Seed is a value used to start a sequence of random numbers
Lecture Summary
Seed is a value used to start a sequence of random numbers
A seed always yields identical sequence of random numbers

15. Tutorial 4 Q3
Moral of the story

16. Tutorial 4 Q4
All non-negative = NOT(there exists one negative)
There exists one negative = NOT(all non-negative)

17. Tutorial 4 Q6
Why time(NULL)?
What is %(high-low+1)?

18. Tutorial 4 Q6

19. PE is soon, recess week is soon
Summary
Repetition
Arrays
Random numbers
#lab2
PE is soon, recess week is soon