COMP2004 Programming Practice Sam Holden Department of Computer Science University of Sydney

About Me Room: Madsen G61 Consultation: 20 mins before each lecture to arrange an appointment during consultation times

Textbook C++ Primer by Lippman 3rd Edition The C++ Programming Language by Stroustrup 3rd Edition Thinking in C++ by Eckel 2nd Edition

Course Information 'Practice of Programming' so expect a some programming Development Tools Library Usage

Lecture Schedule The Basics of C++ Basics of development under Unix The less basic Basics of C++

Assessment Assignment Zero0% Assignment One10% Assignment Two10% Assignment Three20% Final Exam60%

Assignment Policy Machine and Hand marked Individual work, no groups or copying Follow output instructions exactly Must work on department software No late assignments accepted without a medical certificate

The C++ Language C++ is what we will be using C will not be covered (except the parts which are part of C++)

C++ at Basser Using the GNU C++ compiler Usage: –g++ -Wall -g -o hello hello.cc hello.cc is the C++ file The executable will be hello -g adds debugging information -Wall turns on all warnings

A Simple C++ Program C++ starts in a special function called main #include int main() { std::cout << "They killed Kenny\n"; } The above is a complete C++ program

Variables C++ is strongly typed Every variable has a type and must be declared #include int main() { int result = 5 + 4; std::cout<<result<<std::endl; }

Some Built-in Types

Constants Constants are declared with the keyword const const int life = 42; const double pi = ; Constants are just like variables (except not variable)

Operators C++ has a lot of operators There are math operators like +, -, *, /, % Comparison operators like ==, >=,, != Logical operators like ||, &&, ! Bitwise operators like &, |, ~

More Operators a++ and ++a mean a =a+1 (sort of, see your text book for the real story) a-- and --a are similar a+=10 means a=a+10 There are a?=b versions for all the math operators

Enumerated Types An enumeration is a type that can hold a set of values They act lie integer types They are very useful for anything with a restricted domain enum day_of_week { SUN, MON, TUE, WED, THU, FRI, SAT }; day_of_week day; day = WED; day = day_of_week(5); //set to FRI

Writing Functions A function looks like this: double half(int num) { double result; result = num/2.0; return result; } half returns a double It takes a single int argument

Writing Functions II If a function doesn’t return anything it is declared as returning void void display_square(int num) { std::cout << num*num; }

If Statements C++ uses an if statement for selection int main() { char c; std::cin >> c; if (c == 'y') { std::cout << "You typed a y"; }

If Statements II There is also an else if (c == 'y') std::cout << "You typed a y"; else std::cout "You didn't type a y"; Can join an else and an if: if (c == 'y') std::cout <<"You typed a y"; else if (c == 'n') std::cout <<"You typed an n"; else std::cout <<"Only y/n are accepted";

Switch Statements A replacement for multiple ifs: char c; … switch (c) { case 'y' : std::cout << ”A y"; break; case 'n' : std::cout << ”A n"; break; default : std::cout << "y/n only"; } Works with any integral type

Switch Statements II Cases fall thorugh by default char c; … switch (c) { case 'y' : std::cout << ”A y"; case 'n' : std::cout << ”A n"; default : std::cout << "y/n only"; } The above wrong

For Statements for(int i=0;i<10;i++) std::cout << "i is " << i << std::endl; Initialisation : int i=0 Test : i<10 Increment : i++ Body : std::cout <<...

While Statements int i=0; while(i<10) { std::cout << "i is " << i << std::endl; i++; } Test : i<10 Body : between {}s

Do Statements int i=0; do { std::cout << "i is " << i << std::endl; i++; } while (i<10); Similar to while Always executes one Not often used

Arrays Combine well with for int scores[5] = { 1,2,3,4,5}; for (int i=0;i<5;i++) std::cout "Score ” << i << " : ” <<scores[i]; First element has index zero Arrays do not keep track of their length Do not automatically grow

Pointers A hard concept int i = 27; int* p = &i; *p=26; std::cout << i << endl; std::cout << p << endl; std::cout << *p << endl; & takes the address of a variable *p dereferences p source of many bugs

Pointers and Arrays closely related in C++ Can traverse an array with pointers char s[] ={'h','e','l','l','o','\0'}; for (int i=0;s[i]<5;i++) cout << s[i] << endl; for (char *p = s;*p!=0;p++) cout << *p << end; A nul terminated array of chars is a C-style string Note we assigned an array to a pointer and incremented a pointer

C-Style Strings Double quoted strings are C-Style strings We can initialise arrays with them We can assign them to pointers to char We can print them with std::cout char s1[] = "hello"; const char *s2 = "hello”; std::cout << s1 << s2;

Pointers and Const A pointer has two parts –the pointer –what it points to Which one does const apply to? Both are allowed

Pointers and Const Example char s[] = "hello"; char s2[] = "bye-bye"; const char* pc = s; pc[1] = 'a'; //error pc = s2; //ok char* const cp = s; cp[1] = 'a'; //ok cp = s2; //error const char* const cpc = s; cpc[1] = 'a'; //error cpc = s2; //error

References An alternative name for an item Must always reference a valid item Can not switch items Must be initialised when declared Like a pointer that automatically gets dereferenced int i = 42; int &r = i; r++; std::cout << i << std::endl;

Pointers, References and Const References are often used as arguments Pointers are as well If the argument is not modified it should be const char* strcpy(char* dest, const char* src) { char *result = dest; while(*dest++ = *src++) /*nothing*/; return dest; }