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Monday, 21 June 2010

String

String:
  • Strings are character array.
  • Character array are stored in contiguous memory location.
String Constant:
  • A string constant is a one-Dimensional array of characters terminated by a null character('\0').
  • Each character in the array occupies one byte of memory and the last character is always '\0'
    Example:
        char str[]={'C','P','U','\0'};
  • The terminating null character('\0') is very important in a string because its the only way for the compiler to know where the string ends.
Null Character('\0'):
  • '\0' is called null character.
  • '\0' and 0 are not same because both has different ASCII value. ASCII value of '\0' is 0 but ASCII value of 0 is 48.
String Initialization:
  • A string can be initialized without adding the terminating null character as,

        char str[]="WELCOME";

    Here C inserts the NULL character automatically.
Accessing Character array elements:
  • Similar to integer array we can access array elements  
    #include< stdio.h >
    int main()
    {
        int i=0;
        char str[]="WELCOME";
        while(str[i]!='\0')
        {
            printf("%c",str[i]);
            i++;
        }
        return;
    }
  • This can be done by using pointer also. Mentioning th name of the array we get the base address(zeroth element) of the array.
    #include< stdio.h >
    int main()
    {
        char str[]="WELCOME",*ptr;
        ptr=str;
        while(*ptr!='\0')
        {
            printf("%c",*ptr);
            ptr++;
        }
        return;
    }
Reading a string from a keyboard:
  • For reading and writting a string the format specifier is %s and no & is needed
    #include< stdio.h >
    int main()
    {
        char str[30];
        printf("Enter the string\n");
        scanf("%s",str);
        printf("String=%s",str);
        return;
    }

    The scanf() function fills in the character typed at keyboard into the str[] array until the blank space or enter key is hit. If blank space or enter key is hit scanf() automatically place a '\0' in the array.
  • Normally the %s will read a string upto a blank space. To read a muti word string untill the end of line including blank space use %[^\n]s
    #include< stdio.h >
    int main()
    {
        char str[100];
        printf("ENter the string\n");
        scanf("%[^\n]s", str);
        printf("String=%s",str);
        return;
    }

    Output:
    Enter the string
    welcome honey
    String=Welcome honey
  • Other way of reading multiword string is gets() and puts(). But it is dangerous to use gets() in programs so try to avoid gets()
    #include< stdio.h >
    int main()
    {
        char str[30];
        printf("Enter the string\n");
        gets(str);
        puts(str);
        return;
    }
Pointer and String:
  • A string can be stored in 2 forms

    1. char str[]="Welcome"; //here Welcome is stored in a location called str
    2. char *str="Welcome"; //here Welcome is stored in some other location i memory and assign the address of the string in a char pointer
  • The advantage of pointing a string using a character pointer is we cannot assign a string to another string but we can assign a char pointer to another char pointer
    #include< stdio.h >
    int main()
    {
        char str1[]="Welcome",str2[30];
        char *ptr1="Welcome",*ptr2;
        //str2=str1; //error
        ptr2=ptr1;
        printf("ptr2=%s",ptr2);
        return;
    }
  • Once a string has been defined it cannot be initialized to another set of characters but using char pointer we can redefine the string.
    #include< stdio.h >
    int main()
    {
        char str1[]="Welcome";
        char *ptr1="Welcome";
    //  str1="Good";//error
        ptr1="Good";
        printf("ptr1=%s",ptr1);
        return;
    }

     
Points to consider in Strings:
  1. The size of the string depends on the size of declaration not the number of characters in the string
    #include < stdio.h>
    void main()
    {
        char str[30]="Network programming";
        printf("%d",sizeof(str));
    }

    The output here is 30 not 1
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