1. Quiz 1
96/07/23

2. Quiz 1 عدد زیر را به مبنای 2 بنویسید. 100.25
-11 (به روش متمم 2، طول بیتی = 4)
الگوریتم برنامه ای بنویسید که عدد n را دریافت کند و دنباله فیبوناچی را عدد کمتر از n چاپ کند.
برای n = 10 خروجی زیر مورد نظر است:
1 , 1 , 2 , 3 , 5 , 8

4. Control Structures
Lecture 6

5. Outline Control Structures selection structure if if … else
Nested if … else
switch

6. Control Structures
All programs could be written in terms of only three control structures,
sequence structure
Normal operation, definition, etc.
selection structure
if … else, switch, etc.
repetition structure
for, while, do … while.

7. Control Structures Decisions are based on conditions
Do statements based on conditions
True  The statements will be done
False  The statement wont be done

8. Conditions Conditions by comparisons; e.g.,
If a is greater then b
If c equals to d
Comparing numbers: Relational Operators

9. Relations
Relations produce a bool value

10.  You should read the book
Boolean operations
Multiple conditions in decision making
Logical relation between conditions
if you are student and you have the programming course
 You should read the book
C Boolean operators
and &&
or ||
not ! p q
p && q
p || q !p
False
True

11. Boolean operations Examples bool a = true, b=false, c;
c = !a; //c=false
c = a && b; //c=false
c = a || b; //c=true
c = !a || b; //c=false

12. Precede

13. Example

14. Casting In logical operations In mathematical & comparison operations
0  False, non-zero  True
In mathematical & comparison operations
False  0 , True  1

15. Examples  x  [10 , 20] Wrong Version Correct Version Let x = 30
10 <= 30 <=20  (10 <= 30) <= 20
 true <= 20  1 <= 20  true!!!
Correct Version
 (10 <= x) && (x <= 20)
 (10 <= 30) && (30 <= 20)  true && false  false

16. Examples  a,b > 0 Wrong version
 Let a = -10, b = 20
 -10 && 20 > 0  -10 && (20 > 0)
 -10 && true  true && true  true !!!
Correct version
 (a > 0) && (b > 0)
 Let a = -10, b = 20
 (-10 > 0) && (20 > 0)  false && true  false

17. Lazy evaluation(Short-circuit)
When final result is found, does not evaluate remaining
int i
bool a =
true, b
false, c
true; d
a || || c;
= 1;
bool bool
d = b && (a || c);
d = (i > 0) && (sqrt(i)
> 5.6);

18. Selection Structures
C provides three types of selection structures in the form of statements:
The if selection statement either performs (selects) an action if a condition is true or skips the action if the condition is false.
The if…else selection statement performs an action if a condition is true and performs a different action if the condition is false.
The switch selection statement performs one of many different actions depending on the value of an expression.

19. Selection Structures
The if statement is called a single-selection statement because it selects or ignores a single action.
The if…else statement is called a double-selection statement because it selects between two different actions.
The switch statement is called a multiple-selection statement because it selects among many different actions.

20. if statement Decision making in C Expression
if( <expression> )
<statements1> else
<statements2>
Expression
A boolean statement: a <= b +
A mathematical statement: a
zero  false
Non-zero  true
b or a variable: a

21. Type of statements Expression statement Compound statement
Single statements
x = y + 10;
Compound statement
Starts with { and ends with }
 All statements can be between { and }

22. Flowchart if(<expression>) <statement1> else

23. Program to check if number is even or odd

24. Statements in if-else
Empty statement
Block statements

26. More than two choices If statement: 2 choices
If conditions are true  if statements
If conditions are false  else statements
How to make decisions when there are multiple choices?

27. Reminder if( <Condition> ) <command 1> Other command… true
false

28. Reminder
if( <Condition> ) <command 1> else <command 2> Other command…
false
true

29. Reminder
if( <Condition> ) { <command 1> <command 2> } else <command 3> Other command…
false
true

30. More than two choices To avoid repeating conditions in if statements
To avoid running unnecessary statements
Nested if: check multiple conditions
<Statements 1> becomes an if-else statement
<Statements 2> becomes an if-else statement
Repeat it as many as needed

31. Nested if

32. Reminder
if( <Condition 1> ) { <command 1> <command 2> } else if( <Condition 2>) <command 3> else <command 4> Other command…
false
false
true
true

33. Map numeric grade to alphabetic

34. Example 1: Map numeric grade to alphabetic

35. Map numeric grade to alphabetic

36. Map numeric grade to alphabetic

37. Nested if: Example 2
Determine a char is alphabetic, Uppercase or not, numeric, less or greater than 5 or none of them

38. Equivalent if-else

39. Nested if: Incomplete branch
1) else part is optional
2) else always associates with the nearest if
Example:
To avoid error you should close off you code or Use Empty statements

40. Nested if: close off & empty statement

41. switch-case: Multiple choices
Multiple conditions
If-else if-else if-….
Select from alternative values of a variable
switch-case
Values should be constant not expression: i, i+j,
Values & Variables should be int or char
switch(variable) {
case value1:
<statements 1>
case value2:
<statements 2> }

42. How does switch-case work?
Each switch-case can be rewritten by If-else
if-else version of switch-case in the previous slide
if(variable == value1)}
<statements 1>
<statements 2> }
else if(variable == value2){

43. Example
Write a program that get a char, if a or b or c print uppercase of char otherwise print error.

44. Example using switch

45. switch-case
All values used in case should be different switch(i){ //Error case 1: … case 2:

46. switch-case
All values must be value, not expression of variables switch(i){ //Error case j: … case 2: case k+10:

47. switch-case: multiple matches

48. switch-case vs. if-else
if-else is more powerful than switch-case
switch-case is only for checking the values of a variable and the values must be constant
Some if-else cannot be rewritten by switch-case
double var1, var2; if(var1 <= 1.1)
<statements 1>
if(var1 == var2)
<statements 2>

49. Nested switch-case

50. Conditional Expression
Assign value according to conditions A ternary operator Example:

51. Example
Map Alphabetic Grade to Numeric