c++ - calculate length of a string without using standard library funcions(like strlen) or indexing operator [] -

i have started learn c++. want clear no homework question, stuck on.

i going through assignment questions on mit website, , have pasted question here;

write function returns length of string (char *), excluding final null character. should not use standard-library functions. may use arithmetic , dereference operators,but nottheindexing operator([]).

i don't know how without array.

any appreciated!!

this did:

#include<iostream> #include<conio.h> #include<string>   using namespace std;  int stringlength (char* numptr);  int main() {     char *mystring;       cout<<"enter string \n";     cin>>mystring;      cout<<"length "<<stringlength(mystring);      getch(); }  int stringlength (char* numptr) {      int count=0;      for(;*numptr<'\0';*numptr++)     {                    count++;     }     return(count);  }    had done before asked u problem. got me answer of zero.  if in function change *numptr<'\0' *numptr!= 0, right answer.  confused is, isn't null character, why cant check      that. 

first of all, not way learn c++ in 2013. answer relies on low-level pointer manipulation. there lot more important things learn c++ before point. right now, should learning string, vector, functions, classes, , not these low-level details.

to answer question, have know how strings represented. represented array of characters. in c , c++, arrays not have built in length. have store or use other means of finding length. way strings make can find length store 0, last position in array. "hello" stored

{'h','e','l','l','o',0} 

to find length go through array starting @ index 0 , stop when encounter character value of 0;

the code this

int length(const char* str){     int = 0;     for(; str[i] != 0; i++);     return i; }  

now in c , c++ can str[i] same *(str + i); satisfy question can write this

int length(const char* str){     int = 0;     for(; *(str + i) != 0; i++);     return i; }  

now, instead of using + i, can increment str directly;

int length(const char* str){     int = 0;     for(; *str++ != 0; i++){;     return i; }  

now in c, value false if 0, otherwise true, not need != 0, can write

int length(const char* str){     int = 0;     for(; *str++; i++){;     return i; }