C++ For Science and Engineering Lecture 17

Transcription

1 C++ For Science and Engineering Lecture 17 John Chrispell Tulane University Monday October 4, 2010

2 Functions and C-Style Strings Three methods for representing the C-style string: An array of char A quoted sttring constant (or string literal) A pointer-to-char set to the address of the string A three are type pointer to char (or type char *), and work as arguments to string-processing functions. char ghost [ 1 5 ] = g a l l o p i n g ; char s t r = galumphing ; i n t n1 = s t r l e n ( ghost ) ; // ghost i s &ghost [ 0 ] i n t n2 = s t r l e n ( s t r ) ; // p o i n t e r to char i n t n3 = s t r l e n ( gamboling ) ; // a d d r e s s o f s t r i n g In all cases you ar passing a string as an argument, or more accurately you ar passing the address of the first character in the string. John Chrispell, Monday October 4, 2010 slide 3/15

3 Functions and C-Style Strings Remember that C-style strings have a terminating NULL character built in that makes them distinct from plain character arrays. This allows functions to loop over the elements in the C-style string and find the terminating character. Consider the following user defined function. It can be used to count the number of times a specific character is in string. / ================================================ / / This f u n c t i o n c o u n t s the number o f ch c h a r a c t e r s / / i n the s t r i n g s t r / / ================================================ / i n t c i n s t r ( const char s t r, char ch ){ i n t count = 0 ; while ( s t r ){ // q u i t when s t r i s \0 i f ( s t r == ch ){ count++; s t r ++; // move p o i n t e r to next char return count ; A main function is given in the next listing: John Chrispell, Monday October 4, 2010 slide 5/15

4 strgfun.cpp #include <iostream > i n t c i n s t r ( const char s t r, char ch ) ; // i n t c i n s t r ( c o n s t char s t r [ ], char ch ) ; // 2nd p r o t o t y p e. using namespace s t d ; char mmm[ 1 5 ] = minimum ; // s t r i n g i n an a r r a y char w a i l = u l u l a t e ; // w a i l p o i n t s to s t r i n g i n t ms = c i n s t r (mmm, m ) ; i n t us = c i n s t r ( w a i l, u ) ; cout << ms << m c h a r a c t e r s i n << mmm << e n d l ; cout << us << u c h a r a c t e r s i n << w a i l << e n d l ; Joke from text: Why are string processing functions so ruthless? John Chrispell, Monday October 4, 2010 slide 7/15

5 strgfun.cpp #include <iostream > i n t c i n s t r ( const char s t r, char ch ) ; // i n t c i n s t r ( c o n s t char s t r [ ], char ch ) ; // 2nd p r o t o t y p e. using namespace s t d ; char mmm[ 1 5 ] = minimum ; // s t r i n g i n an a r r a y char w a i l = u l u l a t e ; // w a i l p o i n t s to s t r i n g i n t ms = c i n s t r (mmm, m ) ; i n t us = c i n s t r ( w a i l, u ) ; cout << ms << m c h a r a c t e r s i n << mmm << e n d l ; cout << us << u c h a r a c t e r s i n << w a i l << e n d l ; Joke from text: Why are string processing functions so ruthless? Because they stop at nothing. The next example returns a C-style string. John Chrispell, Monday October 4, 2010 slide 7/15

6 strgback.cpp #include <iostream > char b u i l d s t r ( char c, i n t n ) ; // p r o t o t y p e i n t times ; char ch ; cout << Enter a character : ; c i n >> ch ; cout << Enter an i n t e g e r : ; c i n >> times ; char ps = b u i l d s t r ( ch, t i m e s ) ; cout << ps << endl ; delete [ ] ps ; // f r e e memory / Later we w i l l learn about classes and destructors / / That w i l l take care of memory deallocation for us / ps = bui lds tr ( +, 20); // reuse pointer cout << ps << DONE << ps << endl ; delete [ ] ps ; // f r e e memory char buil dst r ( char c, i n t n ){ char p s t r = new char [ n + 1 ] ; p s t r [ n ] = \0 ; // t e r m i n a t e s t r i n g while ( n > 0){ p s t r [ n ] = c ; // f i l l r e s t o f s t r i n g return pstr ; John Chrispell, Monday October 4, 2010 slide 9/15

7 Passing Structurs to Programs. Lets first consider treating a structure like we would a simple type: (like int, or double). We define a simple struct: s t r u c t t r a v e l t i m e { i n t hours ; i n t mins ; A basic prototype for a function of this sort is: t r a v e l t i m e sum ( t r a v e l t i m e t1, t r a v e l t i m e t2 ) ; A simple function that uses these is: John Chrispell, Monday October 4, 2010 slide 11/15

8 travel.cpp #include <iostream > s t r u c t travel time { i n t hours ; i n t mins ; ; const i n t M i n s p e r h r = 6 0 ; t r a v e l t i m e sum ( t r a v e l t i m e t1, t r a v e l t i m e t2 ) ; void show time ( t r a v e l t i m e t ) ; travel time day1 = {5, 45; // 5 hrs, 45 min travel time day2 = {4, 55; // 4 hrs, 55 min t r a v e l t i m e t r i p = sum ( day1, day2 ) ; cout << Two day t o t a l : ; show time ( t r i p ) ; t r a v e l t i m e day3= {4, 32; cout << Three day t o t a l : ; show time (sum ( t r i p, day3 ) ) ; t r a v e l t i m e sum ( t r a v e l t i m e t1, t r a v e l t i m e t2 ){ t r a v e l t i m e t o t a l ; t o t a l. mins = ( t1. mins + t2. mins ) % M i n s p e r h r ; t o t a l. hours = t1. hours + t2. hours + ( t1. mins + t2. mins ) / M i n s p e r h r ; return t o t a l ; void show time ( travel time t ){ cout << t. hours << hours, << t. mins << minutes \n ; John Chrispell, Monday October 4, 2010 slide 13/15

9 strctfun.cpp #i n c lude <iostream > #i n c lude <cmath> / s t r u c t u r e d e c l a r a t i o n s / s t r u c t p o l a r { double distance ; // distance from o r i g i n double angle ; // d i r e c t i o n from o r i g i n ; s t r u c t r e c t { double x ; // h o r i z o n t a l d i s t a n c e from o r i g i n double y ; // v e r t i c a l d i s t a n c e from o r i g i n ; / p r o t o t y p e s / p o l a r r e c t t o p o l a r ( r e c t xypos ) ; void s h o w p o l a r ( p o l a r dapos ) ; re c t r pl a c e ; p o l a r pplace ; cout << Enter the x and y values : ; while ( cin >> r pl ac e. x >> r pl ac e. y ) // s l i c k use of cin { pplace = r e c t t o p o l a r ( r p l a c e ) ; s h o w p o l a r ( p p l a c e ) ; cout << Next two numbers (q to quit ) : ; cout << Done. \ n ; / c o n v e r t r e c t a n g u l a r to p o l a r c o o r d i n a t e s / p o l a r r e c t t o p o l a r ( r e c t xypos ){ p o l a r answer ; answer. d i s t a n c e = s q r t ( xypos. x xypos. x + xypos. y xypos. y ) ; answer. a n g l e = atan2 ( xypos.y, xypos. x ) ; return answer ; // r e t u r n s a p o l a r s t r u c t u r e / show polar coordinates, converting angle to degrees / void s h o w p o l a r ( p o l a r dapos ){ const double Rad to deg = ; cout << d i s t a n c e = << dapos. d i s t a n c e ; cout <<, a n g l e = << dapos. a n g l e Rad to deg ; cout << d e g r e e s \n ; John Chrispell, Monday October 4, 2010 slide 15/15

10 strctptr.cpp It is also possible to pass structs by address. This is useful if you want to update the contents, or initialize them. #include <iostream > #include <cmath> s t r u c t p o l a r { double distance ; // distance from o r i g i n double angle ; // d i r e c t i o n from o r i g i n ; s t r u c t r e c t { double x ; // h o r i z o n t a l d i s t a n c e from o r i g i n double y ; // v e r t i c a l d i s t a n c e from o r i g i n ; // p r o t o t y p e s void r e c t t o p o l a r ( const r e c t pxy, p o l a r pda ) ; void s h o w p o l a r ( const p o l a r pda ) ; re c t r pl a c e ; p o l a r pplace ; cout << Enter the x and y values : ; while ( cin >> r pl ac e. x >> r pl ac e. y ){ r e c t t o p o l a r (& rplace, &pplace ) ; // pass addresses show polar (& pplace ) ; // pass address cout << Next two numbers (q to quit ) : ; cout << Done. \ n ; / show polar coordinates, converting angle to degrees / void s h o w p o l a r ( const p o l a r pda ){ const double Rad to deg = ; cout << distance = << pda >distance ; cout <<, angle = << pda >angle Rad to deg ; cout << d e g r e e s \n ; / c o n v e r t r e c t a n g u l a r to p o l a r c o o r d i n a t e s / void r e c t t o p o l a r ( const r e c t pxy, p o l a r pda ){ pda >d i s t a n c e = s q r t ( pxy >x pxy >x + pxy >y pxy >y ) ; pda >a n g l e = atan2 ( pxy >y, pxy >x ) ; John Chrispell, Monday October 4, 2010 slide 17/15