COMP 3000 ObjectOriented Programming for Engineers and Scientists

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

Chapters • Ch 1, • Ch 2, • Ch 3. 1 and 3. 2 1 -

C++ Variables • C++ Identifiers – – – 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 -

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. 1 -

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. 1 -

Data Types: Display 1. 2 Simple Types (1 of 2) Copyright © 2008 Pearson

Data Types: Display 1. 2 Simple Types (2 of 2) Unsigned Version: unsigned int,

Assigning Data • Initializing data in declaration statement – Results "undefined" if you don’t! • int my. Value = 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 -

Display 1. 3 Some Escape Sequences (1 of 2) Copyright © 2008 Pearson Addison-Wesley.

Constants • Naming your constants – 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 -

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)my. Int / my. Double More typical use; cast operator on variable Copyright © 2008 Pearson Addison-Wesley. All rights reserved. 1 -

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

Console Input/Output • I/O objects cin, cout, cerr • Defined in the C++ library called <iostream> • Must have these lines (called preprocessor 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 -

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 -

Boolean Expressions: Display 2. 1 Comparison Operators • Logical Operators – Logical AND (&&)

Branching Mechanisms • if-else statements – Choice of two alternate statements based on condition expression – Example: if (hrs > 40) gross. Pay = rate*40 + 1. 5*rate*(hrs-40); else gross. Pay = rate*hrs; Copyright © 2008 Pearson Addison-Wesley. All rights reserved. 2 -

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 -

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 -

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 -

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 -

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 -

Even More Math Functions: Display 3. 2 Some Predefined Functions (1 of 2) Copyright

Even More Math Functions: Display 3. 2 Some Predefined Functions (2 of 2) Copyright

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) Copyright © 2008 Pearson Addison-Wesley. All rights reserved. 3 -

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 -

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 -26

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 -

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 3 -28

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; } 3 -29

Programming Exercise 2 Write a C++ function that computer the standard deviation of four scores. Write a main function to call this menu function: 3 -30