1. Bools & Ifs

2. True/False
C++ bool type
Two values: true & false

3. True/False
C++ bool type
Two values: true & false
Printed as 1 and 0

4. 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:

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

6. 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)

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

8. Conditional
If syntax:
if( expression ) statement;

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

10. Evil Error 1
if(grade < 60); cout << "F";

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:
if( expression ) statement1;
else statement2;
Exactly one statement executes

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

17. Evil Error 3
if(grade >= 60); cout << "Pass"; else cout << "You shall not pass"; cout << "try again";

18. Evil Error 3 Always prints "try again" if(grade >= 60);
cout << "Pass"; else cout << "You shall not pass"; cout << "try again";
Always prints "try again"
Else only applies to next statement!

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

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

21. Example Use { } with if/else to group statements:
if(grade < 60) creditsEarned = 0; cout << "F"; //always executes
Need { } to group instructions:
if(grade < 60) { credits += 0; cout << "F"; }

22. Block Guides Never hurts to put { } around if/else body:
if(grade < 60) { cout << "F"; //this is fine }