CS 101 Computer Programming and utilization. Dr Deepak B Phatak Subrao Nilekani Chair Professor Department of CSE, Kanwal Rekhi Building IIT Bombay

Transcription

1 CS 101 Computer Programming and utilization Dr Deepak B Phatak Subrao Nilekani Chair Professor Department of CSE, Kanwal Rekhi Building Bombay Session 20 More on C++ classes Tuesday, October 11, 2011 Session 20, More on classes

2 Overview Review of Class definition and usage Constructor and destructor functions Notion of a stack Defining a class for character stacks Problem of text editing Using the editor commands Important announcements 2

3 Review of class definition for employee class #include <iostream> #include <cstring> using namespace std; // define a class for employee information class employee { char name[60]; float salary; public: void putname (char *nm); void getname (char *nm); void putsalary(float s); float getsalary(); ; 3

4 Sample public functions for employee void employee::putname(char *nm){ strcpy(name, nm); float employee::getsalary(){ return salary; 4

5 Initialization of an object When an object is defined (instantiated), we would like to initialize it, just as we do with variables int m =28; float y =23.52; There is special member function called constructor It has the same name as the class name It is declared and defined as a member function 5

6 Example of a constructor class intpair{ int m; int n; public: intpair (void); intpair (int x, int y); float ratio(); ; intpair :: intpair(void){ m=0; n =0; intpair :: intpair(int x, int y){ m = x; n = y; 6

7 Constructor intpair:: float ratio(){ ; return (float) m/ (float)n; int main(){ int x=25, y=7; float z; intpair p1; intpair p2 (8,6); z= p2.ratio(); cout<< z << endl; 7

8 Notion of a stack 8

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10 Definition of Stack as a programming object Stack is a container in which values can be pushed in, or popped out First-in last-out or Last-in First-out(LIFO) principle Can be implemented using an array Push always at one end Pop always from the same end 10

11 Class stack #define SIZE #include <iostream> #include <cstring> using namespace std; class stack { // define a class for stack of characters char s[size]; int tops; public: static int stackflag; void init(); void push(char c); char pop(); ; 11

12 Stack void stack::push(char c){ if (tops == 10000){ cout << "stack is full" << endl; return; s[tops]=c; tops ++; char stack::pop(){ if (tops == 0){ cout << "stack is empty" << endl; return '*'; tops--; return s[tops]; ; 12

13 Stack void stack::init(){ tops=0; 13

14 Use of stack for editing text in a file 14

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16 Using stack for editing text int main(){ stack lstack, rstack; char text[5000], outtext[5000]; int oldcursor, newcursor, textlength, outtextlength; int i; // sample text for editing strcpy(text,"abcdefghijklmnopqrstuvwxyz"); textlength =strlen(text); cout << "text to be edited is: "<<text <<endl; 16

17 Editing text lstack.init(); rstack.init(); // initialize stacks /* cursor is at the begining of the text initially push the entire text in the right stack first */ for (i = textlength-1; i >=0; i--) rstack.push(text[i]); int cursor =0; int editflag =0; char editcommand, addword[10]; // editcommands movecursor 17

18 Editing // trial code, // take cursor to position 10, // insert "{1234" before that position strcpy (addword, "{1234"); newcursor =10; if (newcursor > cursor){ // shift characters to left stack from rightstack for (i= cursor; i < newcursor ; i++){ lstack.push(rstack.pop()); 18

19 Editing else { // shift characters to right stack from left stack for (i= cursor; i > newcursor; i--){ rstack.push(lstack.pop()); // push characters from the addword to left stack for (i=0; i<strlen(addword); i++){ lstack.push(addword[i]); outtextlength = textlength +strlen(addword); // update cursor value cursor = newcursor+strlen(addword); 19

20 Editing // end of editing, assemble edited text in rstack for (i=cursor; i >0; i--){ rstack.push(lstack.pop()); // get text in the output string and print cout << endl; for (i=0; i < outtextlength; i++){ outtext[i]=rstack.pop(); cout << outtext << endl; return 0; 20

21 Sample execution results $ $c++ class_stackv1.cpp $./a.out Text is: abcdefghijklmnopqrstuvwxyz text length is : 26 shifting all characters to right Word to be added:{1234 with length 6 21

22 Results shifting 10 characters to left stack abcdefghij adding characters from addword {1234 out length: 32 Shifting all characters from left stack to right 4321{jihgfedcba output text is abcdefghij{1234klmnopqrstuvwxyz $ 22