1. Dale Roberts Department of Computer and Information Science, School of Science, IUPUI CSCI 230 Characters and Strings Literals and Variables Dale Roberts, Lecturer Computer Science, IUPUI E-mail: droberts@cs.iupui.edu

2. Dale Roberts Fundamentals of Strings and Characters Characters Building blocks of programs Every program is a sequence of meaningfully grouped characters Character constant An int value represented as a character in single quotes 'z' represents the integer value of z Strings Series of characters treated as a single unit Can include letters, digits and special characters ( *, /, $ ) String literal (string constant) - written in double quotes "Hello" Strings are arrays of characters String a pointer to first character Value of string is the address of first character

3. Dale Roberts Fundamentals of Strings and Characters String declarations Declare as a character array or a variable of type char * char color[] = "blue"; char *colorPtr = "blue"; Remember that strings represented as character arrays end with '\0' color has 5 elements Inputting strings Use scanf scanf("%s", word); Copies input into word[] Do not need & (because a string is a pointer) Remember to leave room in the array for '\0'

4. Dale Roberts Character Pointers String constant acts like a character pointer char *pc = “ABCDE”; /* declare a character pointer variable */ Variable AddressValue constant731‘A’ constant732‘B’ constant733‘C’ constant734‘D’ constant735‘E’ constant736‘\0’ pc800731 char s1[] = “abc”; Variable AddressValue s1[0] 900‘a’ s1[1] 901 ‘b’ s1[2] 902 ‘c’ s1[3] 903 ‘\0’ ‘A’ ‘B’ ‘C’ ‘D’ ‘E’ ‘\0’ 731 732 733 734 735 736 731800

5. Dale Roberts 1100 Example: char s1[] = “abc”; char *s2 = “abc”; f(){ s1[1] = ‘y’; /* OK */ s2[1] = ‘y’; /* wrong (PC is OK)*/ s1 = “test”; /* wrong */ s2 = “test”; /* OK */ } Example: char s3[] = “abcdef”; f1(){ char *s = s3; *s = ‘A’; /* s3[0]=‘A’ */ s = “test”; printf(“%s\n%s\n”,s,s2);} Character 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 s 2001 2002 2003 ‘a’ ‘b’ ‘c’ ‘d’ 2004 ‘e’ s3[0]=‘A’ 2000 2001 2002 2003 ‘a’ ‘b’ ‘c’ ‘d’ 2004 ‘e’

6. Dale Roberts VariableAddressValue constant90‘A’ constant90‘A’ constant91‘B’ constant92‘C’ constant93‘\0’ constant94‘D’ constant95‘E’ constant96‘F’ constant97‘\0’ constant98‘G’ constant99‘H’ Constant 100‘\0’ pc[0] 20090 pc[1] 202 94 pc[2] 204 98 Pointer Arrays Syntax: int *pi[3]; /* pi[0], pi[1], pi[2] */ float *pf[3]; /* pf[0], pf[1], pf[2] */ Example 1: int i=1, j=2, k=3; int *pi[3] = {&i, &j, &k}; Const can not be changedVariableAddressValue i801 j822 k843 pi[0]10080 pi[1]10182 pi[2]10284 Example 2: char *pc[3]={“ABC”, “DEF”, “GH”};

7. Dale Roberts argc and argv In environments those support C, there is a way to pass command- line arguments or parameters to a program when it begin executing. When main is called to begin execution, it is called with two arguments – argc and argv argc : The first (conventionally called argc ) is the number of command- line arguments the program was invoked with argv : The second (conventionally called argv ) is a pointer to an array of character strings that contain the arguments, one per string. Example: if echo is a program and executed on phoenix prompt, such as if echo is a program and executed on phoenix prompt, such as 10 echo hello world 10 echo hello world Command-Line Arguments pointer array argv argc e c h o \0 h e l l o \0 w o r l d \0 null 3

8. Dale Roberts Command-Line Arguments Example: print out the arguments. ex: hello world 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[]) { 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[]) { while (--argc > 0) while (--argc > 0) printf((argc > 1) ? “%s “ ; “%s\n“, *++argv); printf((argc > 1) ? “%s “ ; “%s\n“, *++argv);}