1. COMP 2710 Software Construction Midterm Exam 1 - Review
Dr. Xiao Qin
Auburn University

2. Chapters
Ch 1, 2, 3
Ch 4, 5
Ch 12.1 and 12.2
Please read Ch 1.1 on page 3
1-2 2

3. C++ Variables C++ Identifiers Variables
Keywords/reserved words vs. Identifiers
Must start with a letter or the underscore symbol
The rest must be letters, digits, or the underscore symbol
Case-sensitivity and validity of identifiers
Meaningful names! (see also Page 13)
Variables
A memory location to store data for a program
Must declare all data before use in program
1-3 3

4. Keywords Reserved Words Predefined meaning in C++ Example:
short, long, char,
true, false,
if, else, for, while, class,
private, public,
typedef, static, sizeof,
new, delete,
See Appendix 1 for a complete list of keywords.
Yes.
C++ is case-sensitive
1-4 4

5. Declare a Variable A variable must be declared before it is used!
Tell the compiler what kind of data (i.e., data type) will be stored in the variable
See what will happen when you compile a C++ program where a variable is not declared.
Give an example.
1-5 5

6. Data Types: Display 1.2 Simple Types (1 of 2)
Page 9:
Short to = = 2^ > bits for 2 Bytes -> 8 Bits per Byte
double: commonly used floating-pint number
Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
1-6 6

7. Data Types: Display 1.2 Simple Types (2 of 2)
Char may be treated as an integer type to save space.
Unsigned Version: unsigned int, unsigned long
Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
1-7 7

8. Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
Assigning Data
Initializing data in declaration statement
Results "undefined" if you don’t!
int myValue = 0;
int count = 0, distance = 15, factor = 1;
Assigning data during execution
Lvalues (left-side) & Rvalues (right-side)
Lvalues must be variables
Rvalues can be any expression
Example: distance = rate * time; Lvalue: "distance" Rvalue: "rate * time"
Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
1-8 8

9. Display 1.3 Some Escape Sequences (1 of 2)
Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
1-9 9

10. Constants Naming your constants Use named constants instead
Literal constants are "OK", but provide little meaning
e.g., seeing 24 in a pgm, tells nothing about what it represents
Use named constants instead
Meaningful name to represent data
const int NUMBER_OF_STUDENTS = 24;
const int BRANCH_COUNT = 10, WINDOW_COUNT = 10; //not recommended, a separate line is clearer.
Called a "declared constant" or "named constant"
Now use it’s name wherever needed in program
Added benefit: changes to value result in one fix
1-10 10

11. Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
Type Casting
Two types
Implicit—also called "Automatic"
Done FOR you, automatically 17 / 5.5 This expression causes an "implicit type cast" to take place, casting the 17  17.0
Explicit type conversion
Programmer specifies conversion with cast operator (double)17 / 5.5 Same expression as above, using explicit cast (double)myInt / myDouble More typical use; cast operator on variable
Precision of Calculations
VERY important consideration!
Expressions in C++ might not evaluate as you’d "expect"!
"Highest-order operand" determines type of arithmetic "precision" performed
Common pitfall!
Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
1-11 11

12. Shorthand Operators: Two Options
Post-Increment intVar++
Uses current value of variable, THEN increments it
Pre-Increment ++intVar
Increments variable first, THEN uses new value
"Use" is defined as whatever "context" variable is currently in
No difference if "alone" in statement: intVar++; and ++intVar;  identical result
Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
1-12 12

13. Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
Console Input/Output
I/O objects cin, cout, cerr
Defined in the C++ library called <iostream>
Must have these lines (called pre- processor directives) near start of file:
#include <iostream> using namespace std;
Tells C++ to use appropriate library so we can use the I/O objects cin, cout, cerr
Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
1-13 13

14. Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
Formatting Numbers
"Magic Formula" to force decimal sizes: cout.setf(ios::fixed); cout.setf(ios::showpoint); cout.precision(2);
These stmts force all future cout’ed values:
To have exactly two digits after the decimal place
Example: cout << "The price is $" << price << endl;
Now results in the following: The price is $78.50
Can modify precision "as you go" as well!
Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
1-14 14

15. Boolean Expressions: Display 2.1 Comparison Operators
Logical Operators
Logical AND (&&)
Logical OR (||)
Equality and Relational Operators
Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
2-15 15

16. Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
Branching Mechanisms
if-else statements
Choice of two alternate statements based on condition expression
Example: if (hrs > 40) grossPay = rate* *rate*(hrs-40); else grossPay = rate*hrs;
Like if-else statements in Java
Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
2-16 16

17. Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
The switch Statement
A new stmt for controlling multiple branches
Uses controlling expression which returns bool data type (true or false)
Syntax:
Display page 62 next slide
Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
2-17 17

18. The break and continue Statements
Flow of Control
Recall how loops provide "graceful" and clear flow of control in and out
In RARE instances, can alter natural flow
break;
Forces loop to exit immediately.
continue;
Skips rest of loop body
These statements violate natural flow
Only used when absolutely necessary!
Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
2-18 18

19. Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
Loops
3 Types of loops in C++
while
Most flexible
No "restrictions"
do-while
Least flexible
Always executes loop body at least once
for
Natural "counting" loop
Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
2-19 19

20. Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
File I/O
Stream must be declared like any other class variable: ifstream inStream; ofstream outStream;
Must then "connect" to file: inStream.open("infile.txt");
Called "opening the file"
Uses member function open
Can specify complete pathname
Declare; Open; and Use.
Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
12-20 20

21. Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
Streams Usage
Once declared  use normally! int oneNumber, anotherNumber; inStream >> oneNumber >> anotherNumber;
Output stream similar: ofstream outStream; outStream.open("outfile.txt"); outStream << "oneNumber = " << oneNumber << " anotherNumber = " << anotherNumber;
Sends items to output file
Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
12-21 21

22. Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
Closing Files
Files should be closed
When program completed getting input or sending output
Disconnects stream from file
In action: inStream.close(); outStream.close();
Note no arguments
Files automatically close when program ends
Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
12-22 22

23. Introduction to Functions
Building Blocks of Programs
Other terminology in other languages:
Procedures, subprograms, methods
In C++: functions
I-P-O
Input – Process – Output
Basic subparts to any program
Use functions for these "pieces"
Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
3-23 23

24. Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
Predefined Functions
Libraries full of functions for our use!
Two types:
Those that return a value
Those that do not (void)
Must "#include" appropriate library
e.g.,
<cmath>, <cstdlib> (Original "C" libraries)
<iostream> (for cout, cin)
Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
3-24 24

25. Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
Even More Math Functions: Display 3.2 Some Predefined Functions (1 of 2)
Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
3-25 25

26. Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
Even More Math Functions: Display 3.2 Some Predefined Functions (2 of 2)
Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
3-26 26

27. Random Number Generator
Return "randomly chosen" number
Used for simulations, games
rand()
Takes no arguments
Returns value between 0 & RAND_MAX
Scaling
Squeezes random number into smaller range rand() % 6
Returns random value between 0 & 5
Shifting rand() % 6 + 1
Shifts range between 1 & 6 (e.g., die roll)
See Example: rand.cpp
Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
3-27 27

28. Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
Random Number Seed
Pseudorandom numbers
Calls to rand() produce given "sequence" of random numbers
Use "seed" to alter sequence srand(seed_value);
void function
Receives one argument, the "seed"
Can use any seed value, including system time: srand(time(0));
time() returns system time as numeric value
Library <time> contains time() functions
Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
3-28 28

29. Components of Function Use
3 Pieces to using functions:
Function Declaration/prototype
Information for compiler
To properly interpret calls
Function Definition
Actual implementation/code for what function does
Function Call
Transfer control to function
Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
3-29 29

30. Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
main(): "Special"
Recall: main() IS a function
"Special" in that:
One and only one function called main() will exist in a program
Who calls main()?
Operating system
Tradition holds it should have return statement
Value returned to "caller"  Here: operating system
Should return "int" or "void"
Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
3-30 30

31. Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
Scope Rules
Local variables
Declared inside body of given function
Available only within that function
Can have variables with same names declared in different functions
Scope is local: "that function is it’s scope"
Local variables preferred
Maintain individual control over data
Need to know basis
Functions should declare whatever local data needed to "do their job"
Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
3-31 31

32. Call-by-Value Parameters
Copy of actual argument passed
Considered "local variable" inside function
If modified, only "local copy" changes
Function has no access to "actual argument" from caller
This is the default method
Used in all examples thus far
Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
4-32 32

33. Call-By-Reference Parameters
Used to provide access to caller’s actual argument
Caller’s data can be modified by called function!
Typically used for input function
To retrieve data for caller
Data is then "given" to caller
Specified by ampersand, &, after type in formal parameter list
Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
4-33 33

34. Constant Reference Parameters
Reference arguments inherently "dangerous"
Caller’s data can be changed
Often this is desired, sometimes not
To "protect" data, & still pass by reference:
Use const keyword
void sendConstRef( const int &par1, const int &par2);
Makes arguments "read-only" by function
No changes allowed inside function body
Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
4-34 34

35. Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
Overloading
Same function name
Different parameter lists
Two separate function definitions
Function "signature"
Function name & parameter list
Must be "unique" for each function definition
Allows same task performed on different data
Copyright © 2008 Pearson Addison-Wesley. All rights reserved.

36. Overloading Example: Average
Function computes average of 2 numbers: double average(double n1, double n2) { return ((n1 + n2) / 2.0); }
Now compute average of 3 numbers: double average(double n1, double n2, double n3) { return ((n1 + n2 + n3) / 3.0); }
Same name, two functions
Copyright © 2008 Pearson Addison-Wesley. All rights reserved.

37. Introduction to Arrays
Array definition:
A collection of data of same type
First "aggregate" data type
Means "grouping"
int, float, double, char are simple data types
Used for lists of like items
Test scores, temperatures, names, etc.
Avoids declaring multiple simple variables
Can manipulate "list" as one entity
Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
5-37 37

38. Programming with Arrays
Plenty of uses
Partially-filled arrays
Must be declared some "max size"
Sorting
Searching
Which two variables for each partially filled array?
Size
Number of elements
Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
5-38 38

39. Testing and Debugging Functions
Many methods:
Lots of cout statements
In calls and definitions
Used to "trace" execution
Compiler Debugger
Environment-dependent
assert Macro
Early termination as needed
Stubs and drivers
Incremental development
Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
4-39 39

40. Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
The assert Macro
Assertion: a true or false statement
Used to document and check correctness
Preconditions & Postconditions
Typical assert use: confirm their validity
Syntax: assert(<assert_condition>);
No return value
Evaluates assert_condition
Terminates if false, continues if true
Predefined in library <cassert>
Macros used similarly as functions
Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
4-40 40