//len.c : find length of a string (strlen); 9 different versions!
// 與 strlen(char*) 功能相同 ! 
int len(char x[ ]) {
   int i=0;
   while(x[i]) ++i;
   return i;
}
int len2(char x[ ]) {
   int i=0;
   while(x[i++]); // 先取其值, 再做 ++
   return --i;   // 注意要減 1 喔
}
int len3(char x[ ]) {
   int i= -1;
   while(x[++i]); // 先做 ++, 再取其值
   return i;   // 注意這是正確的!
}
int len4(char x[ ]) {
   int i = 0;
   for( ;; ) {
      if(x[i] == 0) break;
      ++i;
   }
   return i;   // 注意這也是正確的!
}
int len5(char x[ ]) {
   int i;
   for(i=0; ; i++) {
      if(x[i] == 0) break;
   }
   return i;   // 注意這也是正確的!
}
int len6(char x[ ]) {
   int i;
   for(i=0;x[i] != 0; i++);
   return i;   // 注意這也是正確的!
}
int len7(char x[ ]) {
   char*p = x;
   while(*p) ++p;
   return p - x;   // 注意這寫法是正確的!
}
int len8(char *x) {
   char*p = x;
   while(*p) ++p;
   return p - x;   // 注意這寫法是正確的!
}
int len9(char *x) {
   char*p = x;
   while(p[0]) ++p;
   return p - x;   // 注意這寫法是正確的!
}
#include <stdio.h>
int main( ) {
   printf("Length of \"abc\" is %d; ", len("abc"));
   printf("Length of \"\" is %d\n", len(""));
   printf("Length of \"abc\" is %d; ", len2("abc"));
   printf("Length of \"\" is %d\n", len2(""));
   printf("Length of \"abc\" is %d; ", len9("abc"));
   printf("Length of \"\" is %d\n", len9(""));
} /*********
D:\testc> path C:\Dev-Cpp\bin;%path%
D:\testc> gcc len.c
D:\testc> a
Length of "abc" is 3; Length of "" is 0
Length of "abc" is 3; Length of "" is 0
Length of "abc" is 3; Length of "" is 0
=======================================***/