Fundamentals of Strings and Characters

1. Department of Computer and Information Science,School of Science, IUPUI CSCI N305 Characters and Strings Literals and Variables

2. 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. 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. 800 731 731 ‘A’ 732 ‘B’ 733 ‘C’ 734 ‘D’ 735 ‘E’ 736 ‘\0’ Character Pointers • String constant acts like a character pointer char *pc = “ABCDE”; /* declare a character pointer variable */ VariableAddressValue constant 731 ‘A’ constant 732 ‘B’ constant 733 ‘C’ constant 734 ‘D’ constant 735 ‘E’ constant 736 ‘\0’ pc 800 731 char s1[] = “abc”; VariableAddressValue s1[0] 900 ‘a’ s1[1] 901 ‘b’ s1[2] 902 ‘c’ s1[3] 903 ‘\0’

5. 104 ‘t’ 105 ‘e’ 106 ‘s’ 107 ‘t’ 108 s1[] ‘\0’ 1000 ‘a’ 1001 ‘b’ 1002 ‘c’ 1003 ‘\0’ s s3[] 1100 1100 2000 2000 2000 ‘a’ ‘a’ s3[0]=‘A’ 2001 2001 ‘b’ ‘b’ 2002 2002 ‘c’ ‘c’ 2003 2003 ‘d’ ‘d’ 2004 2004 ‘e’ ‘e’ Character Pointers CONSTANT MEMORY AREA (READ ONLY) 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); } s2 800 100 100 ‘a’ 101 ‘b’ 102 ‘c’ 103 ‘\0’ ...

6. 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}; • Example 2: • char *pc[3]={“ABC”, “DEF”, “GH”}; Const can not be changed

7. argv pointer array e c h o \0 argc h e l l o \0 3 null w o r l d \0 Command-Line Arguments • argcandargv • 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 unix prompt, such as 10<user:/home/droberts> echo hello world

8. Command-Line Arguments Example: print out the arguments. ex: hello world main (int argc, char *argv[]) { int i; for (i = 1; i < argc; i++) printf(“%s%c”, argv[i], (i < argc-1) ? ‘ ’ : ‘\n’); } main (int argc, char *argv[]) { while (--argc > 0) printf(“%s%c”, *++argv, (argc > 1) ? ‘ ’ : ‘\n’); } main (int argc, char *argv[]) { while (--argc > 0) printf((argc > 1) ? “%s “ ; “%s\n“, *++argv); }