Getting appropriate hash index C++

Question

I've tried everything. Even java's forumla:

java.lang.String.hashCode():

s[0]*(31^(n-1)) + s[1]*(31^(n-2)) + ... + s[n-1]

I've interpretted this as a sum: Although I am not quite sure what to do with the s[n-1];

int hashmap::hashstr( const char*const str )
{
    int result = 0;
    int i = 0;
    int j = 0;
    int k = 0;
    unsigned n = 0;
    for ( ; str[n] != NULL; ++n ); // how many characters?

    while ( j != n ) // no more characters
    {
        result += str[i] * ( 31 ^ ( n - k ) );
        j++;
        i++;
        k++;
    }
    return result % maxSize;
}

where maxSize is the 10th element in my fixed array size of 11.

What am i doing wrong? SOME of my hash indicies are coming out wrong. Others, correctly. Why is this? So far everyones been like, "Who cares how it works!! Use a template!" Well, I want to understand this..

Answer 1

unsigned n = 0;
for ( ; str[n] != NULL; ++n ); // how many characters?

You know you could just use strlen(str), right?

And the line:

return result % maxSize;

Where's this result from? I don't see any result variable.

Answer 2

s[0](31^(n-1)) + s[1](31^(n-2)) + ... + s[n-1]

In the formula ^ indicates exponentiation, not the bitwise xor operation.
Check out this SO question.

Answer 3

Just going from this code, you could do the following:

void function (const char *str)
{
    while (*str)
    {
        /* process whatever with *str which is the same as str[i] in a for loop */
        str++;
    }
}

Also, you don't need the second const on those const char *const parameters. const char * is fine.