string.ppt

string.ppt

• 1.
  1 Strings
• 2.
  2 Strings • 1-d arraysof type char • By convention, a string in C is terminated by the end-of-string sentinel ‘0’ (null character) • char s[21] - can have variable length string delimited with 0 • Max length of the string that can be stored is 20 as the size must include storage needed for the ‘0’ • String constants : “hello”, “abc” • “abc” is a character array of size 4
• 3.
  3 Character Arrays andStrings char C[8] = { 'a', 'b', 'h', 'i', 'j', 'i', 't', '0' };  C[0] gets the value 'a', C[1] the value 'b', and so on. The last (7th) location receives the null character ‘0’  Null-terminated (last character is ‘0’) character arrays are also called strings  Strings can be initialized in an alternative way. The last declaration is equivalent to: char C[8] = "abhijit";  The trailing null character is missing here. C automatically puts it at the end if you define it like this  Note also that for individual characters, C uses single quotes, whereas for strings, it uses double quotes
• 4.
  4 Reading strings: %sformat void main() { char name[25]; scanf("%s", name); printf("Name = %s n", name); } %s reads a string into a character array given the array name or start address. It ends the string with ‘0’
• 5.
  5 An example void main() { #defineSIZE 25 int i, count=0; char name[SIZE]; scanf("%s", name); printf("Name = %s n", name); for (i=0; name[i]!='0'; i++) if (name[i] == 'a') count++; printf("Total a's = %dn", count); } Satyanarayana Name = Satyanarayana Total a's = 6 Note that character strings read in %s format end with ‘0’ Seen on screen Typed as input Printed by program
• 6.
  6 Differences : array& pointers char *p = “abcde”; The compiler allocates space for p, puts the string constant “abcde” in memory somewhere else, initializes p with the base address of the string constant char s[ ] = “abcde”;  char s[ ] = {‘a’,’b’,’c’,’d’,’e’.’0’}; The compiler allocates 6 bytes of memory for the array s which are initialized with the 6 characters a b c d e 0 a b c d e 0 p S
• 7.
  7 String Constant • Astring constant is treated as a pointer • Its value is the base address of the string char *p = “abc”; printf (“%s %sn”,p,p+1); /* abc bc is printed */ a b c 0 p
• 8.
  8 Library Functions forString Handling  You can write your own C code to do different operations on strings like finding the length of a string, copying one string to another, appending one string to the end of another etc.  C library provides standard functions for these that you can call, so no need to write your own code  To use them, you must do #include <string.h> At the beginning of your program (after #include <stdio.h>)
• 9.
  9 String functions wewill see  strlen : finds the length of a string  strcat : concatenates one string at the end of another  strcmp : compares two strings lexicographically  strcpy : copies one string to another
• 10.
  10 strlen() int strlen(const char*s)  Takes a null-terminated strings (we routinely refer to the char pointer that points to a null-terminated char array as a string)  Returns the length of the string, not counting the null (0) character int strlen (const char *s) { int n; for (n=0; *s!=‘0’; ++s) ++n; return n; } You cannot change contents of s in the function
• 11.
  11 strcat()  char *strcat(char *s1, const char *s2);  Takes 2 strings as arguments, concatenates them, and puts the result in s1. Returns s1. Programmer must ensure that s1 points to enough space to hold the result. char *strcat(char *s1, const char *s2) { char *p = s1; while (*p != ‘0’) /* go to end */ ++p; while(*s2 != ‘0’) *p++ = *s2++; /* copy */ *p = ‘0’; return s1; } You cannot change contents of s2 in the function
• 12.
  12 strcmp() int strcmp (constchar *s1, const char *s2); Two strings are passed as arguments. An integer is returned that is less than, equal to, or greater than 0, depending on whether s1 is lexicographically less than, equal to, or greater than s2.
• 13.
  13 strcmp() int strcmp (constchar *s1, const char *s2); Two strings are passed as arguments. An integer is returned that is less than, equal to, or greater than 0, depending on whether s1 is lexicographically less than, equal to, or greater than s2. int strcmp(char *s1, const char *s2) { for (;*s1!=‘0’&&*s2!=‘0’; s1++,s2++) { if (*s1>*s2) return 1; if (*s2>*s1) return -1; } if (*s1 != ‘0’) return 1; if (*s2 != ‘0’) return -1; return 0; }
• 14.
  14 char *strcpy (char*s1, char *s2); The characters is the string s2 are copied into s1 until 0 is moved. Whatever exists in s1 is overwritten. It is assumed that s1 has enough space to hold the result. The pointer s1 is returned. strcpy()
• 15.
  15 char *strcpy (char*s1, const char *s2); The characters is the string s2 are copied into s1 until ‘0’ is moved. Whatever exists in s1 is overwritten. It is assumed that s1 has enough space to hold the result. The pointer s1 is returned. char * strcpy (char *s1, const char *s2) { char *p = s1; while (*p++ = *s2++) ; return s1; } strcpy()
• 16.
  16 Example: Using stringfunctions 25 9 -1 big sky country beautiful brown cows! int main() { char s1[ ] = "beautiful big sky country", s2[ ] = "how now brown cow"; printf("%dn",strlen (s1)); printf("%dn",strlen (s2+8)); printf("%dn", strcmp(s1,s2)); printf("%sn",s1+10); strcpy(s1+10,s2+8); strcat(s1,"s!"); printf("%sn", s1); return 0; } Output