Dale Roberts

Department of Computer and Information Science,Department of Computer and Information Science,School of Science, IUPUISchool of Science, IUPUI

CSCI 230

Characters and Strings Literals and Variables

Dale Roberts, LecturerComputer Science, IUPUIE-mail: droberts@cs.iupui.edu

Dale Roberts

Fundamentals of Strings and CharactersFundamentals of Strings and Characters

CharactersCharactersBuilding blocks of programsBuilding blocks of programs

Every program is a sequence of meaningfully grouped charactersEvery program is a sequence of meaningfully grouped characters

Character constantCharacter constantAn An intint value represented as a character in single quotes value represented as a character in single quotes'z''z' represents the integer value of represents the integer value of zz

StringsStringsSeries of characters treated as a single unitSeries of characters treated as a single unit

Can include letters, digits and special characters (Can include letters, digits and special characters (**, , //, , $$))

String literal (string constant) - written in double quotesString literal (string constant) - written in double quotes"Hello""Hello"

Strings are arrays of charactersStrings are arrays of charactersString a pointer to first characterString a pointer to first characterValue of string is the address of first characterValue of string is the address of first character

Dale Roberts

Fundamentals of Strings and CharactersFundamentals of Strings and Characters

String declarationsString declarationsDeclare as a character array or a variable of type Declare as a character array or a variable of type char *char *

char color[] = "blue";char color[] = "blue";

char *colorPtr = "blue";char *colorPtr = "blue";

Remember that strings represented as character arrays Remember that strings represented as character arrays end with end with '\0''\0'

colorcolor has has 55 elements elements

Inputting stringsInputting stringsUse Use scanfscanf

scanf("%s", word);scanf("%s", word);

Copies input into Copies input into word[]word[]

Do not need Do not need && (because a string is a pointer) (because a string is a pointer)

Remember to leave room in the array for Remember to leave room in the array for '\0''\0'

Dale Roberts

Character PointersCharacter Pointers

String constant acts like a character pointerString constant acts like a character pointerchar *pc = “ABCDE”; /* char *pc = “ABCDE”; /* declare a character pointer variabledeclare a character pointer variable */ */

VariableVariable AddressAddress ValueValueconstantconstant 731731 ‘A’‘A’constantconstant 732732 ‘B’‘B’constantconstant 733733 ‘C’‘C’constantconstant 734734 ‘D’‘D’constantconstant 735735 ‘E’‘E’constantconstant 736736 ‘\0’‘\0’pcpc 800800 731731

char s1[] = “abc”;char s1[] = “abc”;

VariableVariable AddressAddress ValueValues1[0] s1[0] 900900 ‘a’‘a’s1[1] s1[1] 901 901 ‘b’‘b’s1[2] s1[2] 902 902 ‘c’‘c’s1[3] s1[3] 903 903 ‘\0’‘\0’

‘A’

‘B’

‘C’

‘D’

‘E’

‘\0’

731

732

733

734

735

736

731800

Dale Roberts

1100

ExampleExample::

char s1[] = “abc”;char s1[] = “abc”;char *s2 = “abc”;char *s2 = “abc”;

f()f(){{s1[1] = ‘y’; /* OK */s1[1] = ‘y’; /* OK */s2[1] = ‘y’;s2[1] = ‘y’; /* wrong (PC is OK)*/ /* wrong (PC is OK)*/s1 = “test”;s1 = “test”; /* wrong */ /* wrong */s2 = “test”; /* OK */s2 = “test”; /* OK */

}}ExampleExample::

char s3[] = “abcdef”;char s3[] = “abcdef”;

f1()f1(){{char *s = s3;char *s = s3;*s = ‘A’; /* s3[0]=‘A’ */*s = ‘A’; /* s3[0]=‘A’ */s = “test”;s = “test”;printf(“%s\n%s\n”,s,s2);printf(“%s\n%s\n”,s,s2);

}}

Character PointersCharacter Pointers

‘a’

‘b’

‘c’

‘\0’

100

101

102

103

CONSTANT MEMORY AREA (READ ONLY)

104

105

106

107

‘t’

‘e’

‘s’

‘t’

‘\0’ 108

s1[]1000

1001

1002

1003

‘a’

‘b’

‘c’

‘\0’

100800

s2

...

1100

s3[]2000

s2000

2001

2002

2003

‘a’

‘b’

‘c’

‘d’2004 ‘e’

s3[0]=‘A’2000

2001

2002

2003

‘a’

‘b’

‘c’

‘d’2004 ‘e’

Dale Roberts

VariableVariable AddressAddress ValueValue

constantconstant 9090 ‘A’‘A’constantconstant 9191 ‘B’‘B’constantconstant 9292 ‘C’‘C’constantconstant 9393 ‘\0’‘\0’constantconstant 9494 ‘D’‘D’constantconstant 9595 ‘E’‘E’constantconstant 9696 ‘F’‘F’constantconstant 9797 ‘\0’‘\0’constantconstant 9898 ‘G’‘G’constantconstant 9999 ‘H’‘H’Constant 100Constant 100 ‘\0’‘\0’pc[0] pc[0] 200 200 9090pc[1] pc[1] 202 202 9494pc[2] pc[2] 204 204 9898

Pointer ArraysPointer ArraysSyntax:Syntax:int *pi[3]; int *pi[3]; /* pi[0], pi[1], pi[2] *//* pi[0], pi[1], pi[2] */

float *pf[3]; float *pf[3]; /* pf[0], pf[1], pf[2] *//* pf[0], pf[1], pf[2] */

Example 1Example 1::

int i=1, j=2, k=3; int i=1, j=2, k=3;

int *pi[3] = {&i, &j, &k};int *pi[3] = {&i, &j, &k};

Constcan not bechanged

VariableVariable AddressAddress ValueValue

ii 8080 11

jj 8282 22

kk 8484 33

pi[0]pi[0] 100100 8080

pi[1]pi[1] 101101 8282

pi[2]pi[2] 102102 8484

Example 2:

char *pc[3]={“ABC”, “DEF”, “GH”};

Dale Roberts

argcargc andand argvargv In environments those support C, there is a way to pass In environments those support C, there is a way to pass command-command-line argumentsline arguments or parameters to a program when it begin executing. or parameters to a program when it begin executing.

When main is called to begin execution, it is called with two When main is called to begin execution, it is called with two arguments – arguments – argcargc and and argvargv

argcargc : The first (conventionally called : The first (conventionally called argcargc) is the number of command-) is the number of command-line arguments the program was invoked withline arguments the program was invoked with

argvargv : The second (conventionally called : The second (conventionally called argvargv) is a pointer to an array ) is a pointer to an array of character strings that contain the arguments, one per string.of character strings that contain the arguments, one per string.

ExampleExample::

if if echoecho is a program and executed on phoenix prompt, such as is a program and executed on phoenix prompt, such as 1010 <phoenix:/home/droberts> <phoenix:/home/droberts> echo hello worldecho hello world

Command-Line ArgumentsCommand-Line Arguments

pointer arrayargv

argc

e c h o \0

h e l l o \0

w o r l d \0null3

Dale Roberts

Command-Line ArgumentsCommand-Line Arguments

ExampleExample: print out the arguments. ex: : print out the arguments. ex: hello worldhello worldmain (int argc, char *argv[])main (int argc, char *argv[]){{ int i;int i; for (i = 1; i < argc; i++)for (i = 1; i < argc; i++) printf(“%s%c”, argv[i], (i < argc-1) ? ‘ ’ : ‘\n’);printf(“%s%c”, argv[i], (i < argc-1) ? ‘ ’ : ‘\n’);}}

main (int argc, char *argv[])main (int argc, char *argv[]){{ while (--argc > 0)while (--argc > 0) printf(“%s%c”, *++argv, (argc > 1) ? ‘ ’ : ‘\n’);printf(“%s%c”, *++argv, (argc > 1) ? ‘ ’ : ‘\n’);}}

main (int argc, char *argv[])main (int argc, char *argv[]){{ while (--argc > 0)while (--argc > 0) printf((argc > 1) ? “%s “ ; “%s\n“, *++argv);printf((argc > 1) ? “%s “ ; “%s\n“, *++argv);}}