1. CSE 206
Course Review

2. Conditions Switch If/else-if/else
When: all conditions depend on a single value
Example: switch (var1) { case 1: …; break; default: …; }
If/else-if/else
When: Any other case
Example: if (var1 == 1 || var1 == 2) {...} else if (var > 0) {...} else {...}
Evaluated in order, if first if is not true, then it checks the second “else if”
If more than one condition: check first condition, if true, checks the second

3. Conditions if (a == 1) { if (b == 2) { // …
if (a == 1 && b == 2) // ALWAYS true }
if (a == 1 && b == 2) {
// … }

4. Binary and logical operators
Can be used in any condition (if, loops, …)
Binary
&: and bit by bit
|: or bit by bit
=: assignment, if (a = 1) is ALWAYS true and WILL make a=1, whatever the previous value
...
Logical
&&: and
||: or
==: equal
!=: different …
if (a == b && b != 0)

5. Loops For While Do-while When: you know the number of iterations
Example: for (i = 0; i < n; i++) {...} // initialization; condition; increment
While
When: you DON’T know the number of iterations
Example: while(n > 0) {...} // n must change its value inside the loop!
Do-while
When: you DON’T know the number of iterations but want to execute at least ONCE
Example: do { … } while(n > 0);

6. Functions
Function name
Declare before (outside) main(): int function(int parameter1, int parameter2);
Define (outside main): int function(int p1, int p2) { return p1+p2; }
Call (inside main or other functions): int c = function(a, b);
Why: encapsulate parts of the code that solves one problem for readability and to avoid code duplication
Good example in HW5_Q1, “isdigit(), “isvowel()”, …
(My rule of thumb: any function, including main(), should not be more than ~20 lines of code)
return type
Returns an int

7. Fibonacci: loops vs recursion
Each function call reserves some space in the stack: for each parameter, where to return after the function, function variables. The stack keeps filling until the recursion finishes!
Too many function calls could cause a stack overflow.
fib(5)
fib(4)
fib(3)
fib(3)
fib(2)
fib(2)
fib(1)
fib(2)
fib(1)
fib(1)
fib(1)
fib(1)

8. Fibonacci
Recursive is more readable and intuitive, but it is not the best algorithm to use in this case:
1- It can cause a stack overflow
2- It calculates several times the same result (5 times fib(1), 3 times fib(2), …)
If you are interested:
One optimization for the recursion version could be:
You know the number of Fibonacci numbers you want to print, so you can create an array with those number of positions and initialize all to -1.
Instead of using the base case as n < 2 you could replace it with: if that array position index is different than -1, return the value that it contains.
That way you would only call each function number just ONCE! Less recursive calls and still more readable. This technique is called Memoization.

9. Increment and Decrement Operators
What is the value when i=5
++i vs i++ in:
a = ++i;
a = i++;
What is the difference between:
for (i = 0; i < n; i++)
for (i = 0; i < n; ++i)
What position is accessed in each case:
array[i++]
array [++i]

10. Conditions if (expression1) if (expression2) Statement; else
What could be wrong here?

11. What is the output int main() { int i = 0;
for(i = 0; i < 3; i++); { printf("we are in the loop "); continue; } printf("i=%d\n", i); return 0; }

12. Where is the bug? int arr[20]; for (i = 0; i <= 20; i++){
arr[i] = 0; }
int count;
while (count < 50){
count++; }
char z = ‘p’;
while (z = ‘p’){
z = ‘b’; }
char* s1 = “string”;
char* s2 = “string”;
if (s1==s2){
printf(“We’re equal!\n”); }

13. Pointers in arrays: consecutive in memory
int *end
int *start
int *current
current++
while (current < end) {...}

14. Pointers in LinkedList
a = 1;
next
a = 4;
next
a = 21;
next
a = 8;
next
NULL
Node *head
Second in the list (a=4):
head->next->a = 3;

15. Accessing structs Student s; Student *ptr = &s;
ptr->grades.test1 = 84.1; // through a pointer
s.grades.test2 = 96.2; // through the student
(*ptr).uin = ; // beware of the parenthesis!