C++ For Science and Engineering Lecture 13

Transcription

1 C++ For Science and Engineering Lecture 13 John Chrispell Tulane University Wednesday September 22, 2010

2 Logical Expressions: Sometimes you want to use logical and and logical or (even logical not) in you statements to test several conditions. C++ allows us to do this using the logical and, logical or and logical not operators. Denoted: && // L o g i c a l AND // L o g i c a l OR! // L o g i c a l NOT Note in most cases other than not equal it is clearer to write: i f ( x <= 5) than i f (! ( x > 5 ) ) even if these statements are equal. John Chrispell, Wednesday September 22, 2010 slide 3/31

3 Logical Expressions: The logical AND and logical OR operators have a lower precedence than the relational operators. This means that an expression such as x > 5 && x < 10 i s read as ( x > 5) && ( x < 10) The logical NOT operator has a higer precedence than any of the relational or aritmatic operators.! ( x > 5) // I s i t f a l s e t h a t x i s g r e a t e r than 5?! x > 5 // I s! x g r e a t e r than 5? Logical AND has higer precedence than logical OR. Thus, age > 30 && age < 45 weight > 300 means ( age > 30 && age < 45) weight > 300 John Chrispell, Wednesday September 22, 2010 slide 5/31

4 Logical Expressions: 1 C++ allows you to type the text values and, or, and not for the symbols used in previous examples. 2 These are reserve key words in C++. 3 This advanced format can be used in C as well provided the iso646.h header file is included. The following listing is an example of using the Logical NOT operator. John Chrispell, Wednesday September 22, 2010 slide 7/31

5 not.cpp #include <iostream > #include <c l i m i t s > bool i s i n t ( double ) ; i n t main ( ) { using namespace std ; double num ; cout << Enter an i n t e g e r v a l u e : ; c i n >> num ; while (! i s i n t (num)){ // c o n t i n u e w h i l e num i s not i n t a b l e cout << Out of range p l e a s e t r y again : ; c i n >> num ; i n t val = i n t (num ) ; // typecast cout << You ve e n t e r e d the i n t e g e r << v a l << \nbye\n ; return 0 ; bool i s i n t ( double x ){ i f ( ( x <= INT MAX) && ( x >= INT MIN ) ) { // use c l i m i t s v a l u e s return true ; e l s e { return false ; John Chrispell, Wednesday September 22, 2010 slide 9/31

6 cctype character functions Each function takes a character: isalnum Check if character is alphanumeric isalpha Check if character is alphabetic iscntrl Check if character is a control character isdigit Check if character is decimal digit isgraph Check if character is any printing character other than a space islower Check if character is lowercase letter isprint Check if character is printable (including space) ispunct Check if character is a punctuation character isspace Check if character is a white-space isupper Check if character is uppercase letter isxdigit Check if character is hexadecimal digit tolower Convert uppercase letter to lowercase toupper Convert lowercase letter to uppercase John Chrispell, Wednesday September 22, 2010 slide 11/31

7 cctypes.cpp #i n c lude <iostream > #i n c lude <cctype > // p r o t o t y p e s f o r c h a r a c t e r f u n c t i o n s i n t main ( ) { using namespace std ; cout << Enter text for analysis, and to t e rm i na te i npu t. \ n ; char ch ; i n t w h i t e s p a c e = 0 ; i n t d i g i t s = 0 ; i n t c h a r s = 0 ; i n t punct = 0 ; i n t o t h e r s = 0 ; c i n. get ( ch ) ; // get f i r s t c h a r a c t e r while ( ){ // t e s t f o r s e n t i n e l i f ( isalpha ( ch ) ) // is it an alphabetic character? c h a r s ++; else i f ( isspace ( ch ) ) // is it a whitespace character? w h i t e s p a c e ++; e l s e i f ( i s d i g i t ( ch ) ) // i s i t a d i g i t? d i g i t s ++; else i f ( ispunct ( ch ) ) // is it punctuation? punct++; e l s e o t h e r s ++; c i n. get ( ch ) ; // get next c h a r a c t e r cout << c h a r s << l e t t e r s, << whitespace << whitespace, << d i g i t s << d i g i t s, << punct << punctuations, << o t h e r s << o t h e r s. \ n ; return 0 ; John Chrispell, Wednesday September 22, 2010 slide 13/31

8 The?: Operator C++ has one operator that takes three operands, and can be used to replace the if else statement. e x p r e s s i o n 1? e x p r e s s i o n 2 : e x p r e s s i o n 3 if expression1 is true then the value of the whole conditional is expression2. Otherwise it takes on the value of expression3. 5 > 3? 10 : 1 2 ; // Has v a l u e 10 3 == 9? 25 : 1 8 ; // Has v a l u e 18 John Chrispell, Wednesday September 22, 2010 slide 15/31

9 condit.cpp #i n c l u d e <i o s t r e a m > i n t main ( ) { using namespace std ; / ========================= / / A max f u n c t i o n / / ========================= / i n t a, b ; cout << Enter two i n t e g e r s : ; c i n >> a >> b ; cout << The l a r g e r o f << a << and << b ; i n t c = a > b? a : b ; // c = a i f a > b, e l s e c = b cout << i s << c << endl ; / ========================= / / Fancy P r i n t Statement / / ========================= / const char x [ 2 ] [ 2 0 ] = { Jason, at your s e r v i c e \n ; const char y = Q u i l l s t o n e ; f o r ( i n t i = 0 ; i < 3 ; i ++){ cout << ( ( i < 2)?! i? x [ i ] : y : x [ 1 ] ) ; return 0 ; John Chrispell, Wednesday September 22, 2010 slide 17/31

10 The switch statement You can extend the if else if else sequence by using the C++ switch statement. switch ( i n t e g e r e x p r e s s i o n ){ case l a b e l 1 : s t a t e m e n t ( s ) case l a b e l 2 : s t a t e m e n t ( s )... d e f a u l t : s tatement ( s ) Consider the following example! John Chrispell, Wednesday September 22, 2010 slide 19/31

11 switch.cpp #include <iostream > using namespace std ; void showmenu ( ) ; // f u n c t i o n p r o t o t y p e s void r e p o r t ( ) ; void comfort ( ) ; i n t main ( ) { showmenu ( ) ; i n t choice ; cin >> choice ; while ( c h o i c e!= 6) { switch ( c h o i c e ) { case 1 : cout << None o f the Homework i s graded! \ n ; break ; case 2 : r e p o r t ( ) ; break ; case 3 : cout << A l l the Homework i s graded. \ n ; break ; case 4 : case 5 : comfort ( ) ; break ; d e f a u l t : cout << That s not a c h o i c e. \ n ; showmenu ( ) ; cin >> choice ; cout << Bye! \ n ; return 0 ; void showmenu ( ) { cout << P l e a s e e n t e r 1, 2, 3, 4, or 5 : \ n 1) alarm 2) r e p o r t \n 3) a l i b i 4) comfort \n 5) comfort 2 6) q u i t \n ; void r e p o r t ( ) { cout << It s been an excellent week for C++.\n All students did homework. No one i s f a i l i n g. \ n ; void comfort ( ) { cout << Your s t u d e n t s t h i n k you are the f i n e s t C++ t e a c h e r e v e r! \ n They w i l l a l l go on to be g r e a t programmers. \ n ; John Chrispell, Wednesday September 22, 2010 slide 21/31

12 enum.cpp Enumerators can be used as labels for switch case statements. #i n c l u d e <iostream > i n t main ( ) { using namespace std ; / c r e a t e named c o n s t a n t s f o r 0 6 / enum { red, orange, yellow, green, blue, v i o l e t, i n d i g o ; cout << Enter color code (0 6): ; i n t code ; c i n >> code ; while ( code >= red && code <= i n d i g o ){ switch ( code ){ case red : cout << Her l i p s were red. \ n ; break ; case orange : cout << Her h a i r was orange. \ n ; break ; case y e l l o w : cout << Her shoes were y e l l o w. \ n ; break ; case green : cout << Her n a i l s were green. \ n ; break ; case blue : cout << Her s w e a t s u i t was blue. \ n ; break ; case v i o l e t : cout << Her e y e s were v i o l e t. \ n ; break ; case i n d i g o : cout << Her mood was i n d i g o. \ n ; break ; cout << Enter color code (0 6): ; c i n >> code ; cout << Bye\n ; return 0 ; John Chrispell, Wednesday September 22, 2010 slide 23/31

13 Break and continue statements The break and continue statements allow a program to skip over parts of the code. The break and continue statements may be used in loops allowing the program to jump over statements: while ( c i n. get ( ch ) ) { // ( ) s t a t e m ent 1 i f ( ch == \n ) continue ; // Jumps to ( ) s t a t e m ent 2 s t a t e m ent 3 / c o n t i n u e s k i p s the r e s t o f the body and s t a r t s a new c y c l e / / / while ( c i n. get ( ch ) ) { s t a t e m ent 1 i f ( ch == \n ) break ; // Jumps to (+++) s t a t e m ent 2 s t a t e m ent 3 // (+++) / break s k i p s the r e s t of the loop and goes on to the next statement / John Chrispell, Wednesday September 22, 2010 slide 25/31

14 jump.cpp #i n c l u d e <iostream > const i n t A r S i z e = 8 0 ; i n t main ( ) { using namespace std ; char l i n e [ A r S i z e ] ; i n t s p a c e s = 0 ; cout << Enter a l i n e o f t e x t : \ n ; c i n. get ( l i n e, A r S i z e ) ; cout << Complete l i n e : \ n << l i n e << e n d l ; cout << L i n e through f i r s t p e r i o d : \ n ; f o r ( i n t i = 0 ; l i n e [ i ]!= \0 ; i ++){ cout << l i n e [ i ] ; // d i s p l a y c h a r a c t e r i f ( l i n e [ i ] ==. ) // q u i t i f i t s a p e r i o d break ; i f ( l i n e [ i ]!= ) // s k i p r e s t o f l o o p continue ; s p a c e s ++; cout << \n << spaces << spaces \n ; cout << Done. \ n ; return 0 ; We are going to forget that C and C++ have goto statements. John Chrispell, Wednesday September 22, 2010 slide 27/31

15 cinfish.cpp #i n c l u d e <i o s t ream > const i n t Max = 5 ; i n t main ( ) { using namespace std ; double f i s h [Max ] ; cout << Please enter the weights of your f i s h. \ n ; cout << You may e n t e r up to << Max << f i s h <q to terminate >.\n ; cout << f i s h #1: ; i n t i = 0 ; while ( i < Max && c i n >> f i s h [ i ] ) { i f (++ i < Max){ cout << f i s h # << i +1 << : ; / =================== / / c a l c u l a t e a v e r a g e / / =================== / double t o t a l = 0. 0 ; f o r ( i n t j = 0 ; j < i ; j ++){ t o t a l += f i s h [ j ] ; / =================== / / r e p o r t r e s u l t s / / =================== / i f ( i == 0){ cout << No f i s h \n ; e l s e { cout << t o t a l / i << = a v e r a g e weight o f << i << f i s h \n ; cout << Done. \ n ; return 0 ; The above listing is an example of using non numeric data to teminat a loop. As cin gives an error if inproper values are read. John Chrispell, Wednesday September 22, 2010 slide 29/31

16 user input If the user of a program enters the wrong data. We need to take three steps: Reset cin to accept ne input. Get rid of the bad data. Prompt the user to try again. We reset cin by using the member function clear. Consider the following: John Chrispell, Wednesday September 22, 2010 slide 31/31

17 cingolf.cpp / ========================================== / / example where non numeric input i s skipped / / ========================================== / #include <iostream > const i n t Max = 5 ; i n t main ( ) { using namespace std ; // get data i n t g o l f [ Max ] ; cout << Please enter your g o l f s c o r e s. \ n ; cout << You must e n t e r << Max << rounds. \ n ; i n t i ; f o r ( i = 0 ; i < Max ; i ++){ cout << round # << i +1 << : ; while (! ( c i n >> g o l f [ i ] ) ) { c i n. c l e a r ( ) ; // r e s e t i n p u t while ( c i n. get ( )!= \n ) continue ; // get r i d o f bad i n p u t cout << Please enter a number : ; // c a l c u l a t e a v e r a g e double t o t a l = 0. 0 ; f o r ( i = 0 ; i < Max ; i ++) t o t a l += g o l f [ i ] ; // r e p o r t r e s u l t s cout << total / Max << = average score << Max << rounds \n ; return 0 ; John Chrispell, Wednesday September 22, 2010 slide 33/31