1. CSE 1020:Control Structure
Mark Shtern

2. Selection

3. Flow of Control
Flow of control refers to order in which statements are executed
Sequence flow S1 S2 S3

4. Flow of Control
Selection flow S2
S2.1 S4 S1 S3
S3.1

5. Flow of Control
Selection flow
True S2
S2.1 S4 S1 S3
S3.1
False

6. Flow of Control Selection flow If (condition) { statement-S2}
else
statement-S3
statement-S3.1
True S2
S2.1 S4 S1 S3
S3.1
False

7. If statement
If (count > maximum) { count--; output.println(“Maximum exceeded.”); }

8. Example 5.1
Write a fragment that prompts for and reads an integer from the user and outputs its absolute value without using Math.abs

9. Answer
output.print(“Enter an integer...”); int entry = input.nextInt(); int absValue = entry; If (entry < 0 ) { absValue = - entry; } output.println(absValue);

10. Example 5.2
Rewrite solution of previous Example such that no defaults are used.

11. Answer
output.print(“Enter an integer...”); int entry = input.nextInt(); int absValue; if (entry < 0) { absValue = -entry; } else absValue = entry; output.println(absValue);

12. Building the Condition
Relational Expression
Boolean Variable
Boolean-Returning Method
Boolean Expression
Operator
Syntax
true if ! !x
x is false
&&
x && y
x and y are both true ||
x|| y
either x or y or both are true

13. deMorgan law
!(A && B) is equivalent to (!A) || (!B) !(A || B) is equivalent to (!A) && (!B)

14. Examples if (x >= a && x <b) If (!(x >= a && x <b) )
If (x.equals(y)) vs if (x!=null && x.equals(y))

15. Example 5.3
Write a fragment that determine whether a given integer y is a multiple of a given integer x, and output message accordingly. Note that no integer is a multiple of zero.

16. Answer
If ( x == 0 || y % x !=0) { output.println(“”Not a multiple.”); } else ouput.println(“Yes, it is a multiple”);

17. Multiway if
Statement-S If (condition-1) { Statements-A } else if (condition-2) Statements-B } else if (condition-3) Statements-C } Statements-X

18. Example 5.5
Write a program that prompts for and reads an year (an int) from a user. If the entry is not positive, the program crash. Otherwise, it should output a messages that indicates whether the year entered is a leap year

19. Nested IF
if ( x<=a && y >d)
if ( x<=a) {
if (y >d) }

20. Switch
If (gender == ‘M’) { male++; } else if (gender == ‘F’) female++; } else other++; }
switch (gender) {
case ‘M’:
male++
break;
case ‘F’:
female++;
default:
other++; }

21. Predict results (Ex505)
int x =1; boolean b1 = (x > 0); boolean b2 = false; boolean b3 = b1 && !b2; If (b3 || x == 1) { x++; }

22. Predict results (Ex506)
int x =1; int y = -1; If (x >=y && y > 0) { x++; y = x; } else if (x == y || y < 1) { x--; } else { y = 0; }