C Arrays
=======================================================================================
#include <stdio.h>   
main() {
   int a[4];           /* a is an address constant (the address of a[0])       */
                       /* space for four ints (16 or 32 bytes) reserved        */
   int *pa;            /* pa is an address variable that must point to an int  */
                       /* space for a single address (4 or 8 bytes) reserved   */   
   pa = a;             /* variable = constant (like i = 1234)                  */
   a[0] = 100;         /* array subscripts start a 0                           */
   *(a+1) = 101;       /* *(a+1) same as a[1]                                  */
   pa[2] = 102;        /* since pa = a, pa[2] = a[2]                           */
   *(pa+3) = 103;      /* *(pa+3) == *(a+3) == pa[3]  ==  a[3] so              */
                       /*   pa+3  ==   a+3  == &pa[3] == &a[3]                 */
}
======================================================================================
1. Character arrays are simply byte arrays that must include a byte with a value
   of zero to mark the end of the array.

2. The first eight statements are equivalent.

   char str[4] = "ABC"                /* Need one byte for the terminating zero     */             
   char str[]  = "ABC"                /* Four bytes reserved and initialized        */
   char str[4] = {65, 66, 67, 00);    /* ASCII codes for A, B, C, an null           */
   char str[]  = {65, 66, 67, 00);    /* ASCII codes for A, B, C, and null          */
   char str[4] = {0x41, 0x42, 0x43, 0x00);  /* ASCII codes in hex                   */ 
   char str[]  = {0x41, 0x42, 0x43, 0x00);  /* ASCII codes in hex                   */
   char str[]  = {'A', 'B', 'C', '\0');  /* Chacter (not string) constant           */
   
   char  ok[4]  = "AB"                /* Four bytes reserved, three initialized     */

   char bad[4]  = {65, 66}            /* Four bytes reserved, only two initiallized */
   char bad[]  = {65, 66, 67};        /* Only three reserved, no termination zero   */
   char bad[4] = {65, 66, 67};        /* Four reserved, but last not initialized    */
   char bad[3] = "ABC";               /* compiler will catch this                   */
   char bad[4] = 'ABC';               /* and this                                   */
======================================================================================
cis-lclient03:~/2012/chap2>more strlen1.c
/* Compute the length of a string */
#include <stdio.h>
int strlen(char s[]);
int main()
{
    char line[100] = "This length of this string is ";
    printf("%s%d\n", line, strlen(line));
    return 0;
}
/* strlen: return length of s */
int strlen(char s[])
{
    int i;
    i = 0;
    while (s[i] != '\0')
        ++i;
    return i;
}
cis-lclient03:~/2012/chap2>gcc strlen1.c
cis-lclient03:~/2012/chap2>./a.out
This length of this string is 30
cis-lclient03:~/2012/chap2>
======================================================================================
/* alternate version of strlen: return length of s */
int strlen(char *s)
{
    int n;
    for (n = 0; *s != '\0'; s++)
        n++;
    return n;
}
======================================================================================
/* yet another version of strlen: return length of s */
int strlen(char *s)
{
    char *p = s;
    while (*p != '\0');
        p++;
    return p - s;
}
======================================================================================