CPSC 230 Computers and Programming I Spring 2003 Dr. Lynn Lambert

This course will teach you: C++ Object-oriented concepts Programming Some stabs at problem solving

How computers work Computers understand machine language only Each computer has its own language All computer languages are in binary (1s and 0s) No computer understands English, Powerpoint, or C++

A computer program: Add X to Y and store in Z In machine language: (already simplified to decimal) HUH!?

Assembly Each machine instruction has matching, more English-like assembler: Load X (was: ) Load Y (was: ) Add X Y Z (was: ) Store Z (was: ) Better, but … all this for one addition!?

C++ z=x+y; Much better! BUT, no machines understand source code. Only machine code.

Designing a Program 1. Decide the problem to solve. 2. Design the solution. 3. Translate design to C++ 4. Type the C++ program (source code) using an editor (emacs): program.cc 5. Compile (g++). Translates C++ into machine language (object, machine, executable code) 6. Link (g++). Creates executable. Can be done with step 5 or separately. 7. Run the program (after 1-6).

At each step: 1.Think 2.Do 3.Debug 4.Test

Write a program to calculate the volume of a sphere Problem well-defined Design solution: Read radius Calculate volume (V = 4/3(pi)r 3 Print answer

C++ Program #include // allows reading in and out using namespace std; // standard namespace int main() { float radius; // radius of a sphere float volume; // volume of sphere Float is decimal. // other types are int, char, bool, double

const float mypi = ; // const values cannot be // changed. M_PI also defined in cmath cout << “This program calculates the volume “ << “of a sphere given its radius.” << endl; // lots of other ways to do this cout. cout “; cin >> radius; // volume = 4/3 p r 3 try 1: volume = 4/3 M_PI r …? 3? try 2: volume = 4 / 3 * M_PI * r * r; try 2.b: volume = 4/3 * M_PI * pow(r, 3); // in cmath cout << "The volume of a sphere with radius "; cout << radius << " is " << volume << endl; return EXIT_SUCCESS; // in }

great. except it doesn't work.

Functions (modified from Deitel & Deitel web page)

Why functions? divide and conquer repeatable. reuse reliable code encapsulated

Program Components in C++ Modules: functions and classes Programs use new and “prepackaged” modules New: programmer-defined functions, classes Prepackaged: from the standard library Functions invoked by function call Function name and information (arguments/parameters) it needs Function definitions Only written once

Program Components in C++ Boss to worker analogy A boss (the calling function or caller) asks a worker (the called function) to perform a task and return (i.e., report back) the results when the task is done

Library Functions Functions called by writing functionName(argument1, argument2, …); Perform common mathematical calculations Include the header file Call the appropriate function

Library Functions Example volume = 4.0 / 3.0 * M_PI * pow(r, 3); pow (exponentiation) function returns base exponent (pow(2,3) would return 8) Other math functions listed on p. 173 of text All functions in math library return a double

Parameters/Arguments Function arguments can be Constants sqrt( 4 ); Variables sqrt( x ); Expressions sqrt( sqrt( x ) ) ; sqrt( 3 - 6x );

Other libraries Perform string operations, include Perform character manipulations, include file handling, standard constants and routines Lots of others

Writing your own functions To call a function, you need: Function call – invokes function execution To write your own function, you need: Function call(e.g., pow, sqrt). We know this. Function prototype (shown in function libraries, like -- contains interface information) Function definition– contains the C++ that defines how that function will be executed (e.g., main). Really, we know this.

function call, prototype Calling/invoking a function square(x); Parentheses an operator used to call function Pass argument x Function gets its own copy of arguments After finished, passes back result Function prototype Tells compiler argument(s) type and return type of function int square( int ); Function takes an int and returns an int Explained in more detail later

Function definition Format for function definition return-value-type function-name ( parameter-list ) { declarations and statements } Parameter list Comma separated list of arguments Data type needed for each argument If no arguments, use void or leave blank Return-value-type Data type of result returned (use void if nothing returned)

function definition Example function int square( int y ) { return y * y; } return keyword Returns data, and control goes to function’s caller If no data to return, use return; Function ends when reaches right brace Control goes to caller Functions cannot be defined inside other functions

// Fig. 3.3: fig03_03.cpp. But modified from code in book // Creating and using a programmer-defined function. #include using namespace std; // modified from code in book int square( int ); // function prototype int main() { int number; // Ask user for number square then square that number cout << “This program calculates the square of an integer.” << endl; cout “; cin >> number; // next line is function call cout << number << “ squared is “ << square( x ) << endl; return EXIT_SUCCESS; // indicates successful termination } // end main Parentheses () cause function to be called. When done, it returns the result. Function prototype: specifies data types of arguments and return values. square expects and int, and returns an int.

function header: return type function name, parameter list. // this continues program begun on previous slide // square function definition returns // square of an integer int square( int y ) // y is a copy of argument to function { return y * y; // returns square of y as an int } // end function square OR int square(int nbr) { int answer; answer = nbr * nbr; return answer; } function body: C++ statements in between {}s.

Function Prototypes Function prototype contains Function name Parameters (number and data type) Return type ( void if returns nothing) Only needed if definition after function call semicolon (unlike header in function definition) Prototype must match function definition Function prototype int sqr(int); Function Definition int sqr(int y) { … }

Functions with empty parameter lists Empty parameter lists void or leave parameter list empty Indicates function takes no arguments Function print takes no arguments and returns no value void print(); void print( void );

print function example Prototype void printinfo(void); Function call int main () {... printinfo(); … }

print function example cont'd function definition void printinfo() { cout << "this program calculates"; cout << " the area of a sphere"; cout << endl; }

Function overloading Functions with same name and different parameters Should perform similar tasks i.e., function to square int s and function to square float s int square( int x) {return x * x;} float square(float x) { return x * x; } Similar to overloaded +, /, etc. operators

Function overloading cont'd Overloaded functions distinguished by signature Based on position, number, and type of parameters (order of parameters matters) Name mangling Encodes function identifier with parameters Type-safe linkage Ensures proper overloaded function called

// Fig. 3.25: fig03_25.cpp 2 // Using overloaded functions. 3 #include 4 5 using std::cout; 6 using std::endl; 7 8 // function square for int values 9 int square( int x ) 10 { 11 cout << "Called square with int argument: " << x << endl; 12 return x * x; } // end int version of function square // function square for double values 17 double square( double y ) 18 { 19 cout << "Called square with double argument: " << y << endl; 20 return y * y; 21 } // end double version of function square 23

24 int main() 25 { 26 int intResult = square( 7 ); // int version called 27 double doubleResult; 28 doubleResult = square( 7.5 ); // calls double version 29 cout << "\nThe square of integer 7 is " << intResult 30 << "\nThe square of double 7.5 is " 31 << doubleResult << endl; return 0; // indicates successful termination } // end main Called square with int argument: 7 Called square with double argument: 7.5 The square of integer 7 is 49 The square of double 7.5 is 56.25

Write a program Write a program that uses functions Talk to your neighbors Use the book Use your notes