1. Auburn University http://www.eng.auburn.edu/~xqin
COMP 3000 Object-Oriented Programming for Engineers and Scientists Programmer-Defined Functions
Dr. Xiao Qin
Auburn University

2. Chapters
Ch 1,
Ch 2,
Ch 3.1 and 3.2
Please read Ch 1.1 on page 3
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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
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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
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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.
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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
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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
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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"
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9. Display 1.3 Some Escape Sequences (1 of 2)
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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
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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!
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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
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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
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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!
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15. Boolean Expressions: Display 2.1 Comparison Operators
Logical Operators
Logical AND (&&)
Logical OR (||)
Equality and Relational Operators
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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
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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
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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!
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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
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20. 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"
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21. 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)
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22. Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
Even More Math Functions: Display 3.2 Some Predefined Functions (1 of 2)
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23. Copyright © 2008 Pearson Addison-Wesley. All rights reserved.
Even More Math Functions: Display 3.2 Some Predefined Functions (2 of 2)
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24. 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
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25. 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
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26. 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
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27. 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"
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28. Programming Exercise 1
Write a C++ function that display the calculator menu. The program will prompt the user to choose the operation choice (from 1 to 5). Then it asks the user to input two integer vales for the calculation. See the sample below. Write a main function to call this menu function:
MENU
1. Add
2. Subtract
3. Multiply
4. Divide
5. Modulus
Enter your choice: 1
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29. Programming Exercise 1 int displaymenu(){ int choice;
cout<<" MENU ” << "\n";
cout<<" 1.Add"<<"\n";
cout<<" 2.Subtract"<<"\n";
cout<<" 3.Multiply"<<"\n";
cout<<" 4.Divide"<<"\n";
cout<<" 5.Modulus"<<"\n";
cin >> choice
return choice; }
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30. Programming Exercise 2
Write a C++ function that computer the standard deviation of four scores. Write a main function to call this menu function:
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