1. Bools & Ifs

2. Control Structures Normal execution is sequential Control structures
Selection (branching): making a choice
Repetition (iteration): looping

3. Relational Operators Relational operators :
Binary operators – compare two values
Evaluate to true or false

4. Examples Samples: Notes: 8 < 15 evaluates to true
6 != 6 evaluates to false
2.5 > 5.8 evaluates to false
5.9 <= 7.5 evaluates to true
Notes:
! means "not"
< or > always before = (no => operator)

5. True/False C++ bool type Two values: true (1) & false (0)
bool enrolled = true; //same as = 1 cout << enrolled;

6. True/False C has no bool C++ converts numbers to bools in same way:
Uses integers : 0 = false, all others = true
C++ converts numbers to bools in same way:
bool enrolled = 3.2; //true bool enrolled = 23; //true bool enrolled = -4; //true bool enrolled = 2 - 2; //false

7. Relational Evaluation
Can store result of relational operator:
bool result = 5 < 9; cout << result; Outputs 1 (true)
bool result = 5 == 9; cout << result; Outputs 0 (false)

8. Relational Operators
Conditional statements: only executed if certain conditions are met
if( score is greater than or equal to 90 )
print "Grade is A"

9. One-Way Selection One-way selection syntax:
Expression true  execute statement
Expression false  skip statement

10. If Example Indent statement! Example: int grade; //read grade
if(grade < 60)
cout << "F";
Indent statement!

11. Evil Error 1 if(grade < 60); cout << "F"; Always prints F
If grade < 60 do empty statement (;)
No matter what, print F

12. Evil Error 2
if (x = 5) cout << "Is 5" << endl;

13. Evil Error 2 if (x = 5) cout << "Is 5" << endl;
Changes x to 5
Value of assignment is 5  true
Linux Hack Attempt: if ((options == (__WCLONE|__WALL)) && (current->uid = 0))

14. Evil Error 2
Yoda style (constant first) prevents this error: if (5 == x) cout << "Is 5" << endl;

15. Two-Way Selection Two-way selection syntax:
Expression true  execute statement1
Expression false  execute statement2
Only 1 of the 2 statements executes

16. If Example Example: int grade; //read grade if(grade < 60)
cout << "F";
else
cout << "Pass";

17. Compound (Block of) Statements
Compound statement (block of statements):
Surrounded by { }
Acts as one statement

18. If Example Indent statements! Example:
int grade; double credits; //read grade
if(grade < 60) cout << "F"; else { credits += 4; cout << "Pass"; }
Indent statements!

19. Bad Block Example: Need { } to group instructions:
if(grade < 60) credits += 0; cout << "F"; //always executes
Need { } to group instructions:
if(grade < 60) { credits += 0; cout << "F"; }

20. Block Guides When in doubt, use { } Same line { prevents accidental ;
if(grade < 60) { cout << "F"; //this is fine }
Same line { prevents accidental ;
if(grade < 60); { cout << "F"; //always happens }