String, null-termination and/or strlen issue

Hello all. This is definitly the best site for help on c projects. ( Looking at Adak, Laserlight, Grumpy ....) The program description is in the comment at the head of the source code. Basically it converts any integer from base 10 into a base of the user's choosing. Im having a problem at line 54 when I set variable "J" to "strlen( s ) -1". It returns -1, which means its reading my string as zero. Any suggestions?

Code:

---

/* Write a function itob(n,s,b) that converts the integer
 * n into a base b character representation in the string
 * s. In particular, itob(n,s,16) formats n as a hexadecimal
 * integer in s.
 */

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

void itob( int , char * , int );
int strtoi( char * );
void reverse( char * );
char * find_space( int , int );

int main( int argc , char **argv ){
   
    if( argc != 3 )
        /* expects two arguments, num and new base */
        printf( "Usage: %s n b\nConvert base-10 number [n] into base-[b] number\n" , argv[ 0 ] );
    else{
        int n , b;
        char * string = NULL;
        if( !( n = strtoi( argv[ 1 ] ) ) || !( b = strtoi( argv[ 2 ] ) ) )
            puts( "Invalid integer(s) has been detected...abort" );
        else{
            string = find_space( n , b );
            itob( n , string , b );
            printf( "%s\n" , string );
            getchar();
        }
    }
   
    return 0;
}
int strtoi( char * str ){
    int n , i;
    for( i = 0 , n = 0;str[ i ] != '\0' && str[ i ] <= '9' && str[ i ] >= '0' ; ++i )
        n = n * 10 + ( str[ i ] - '0' );
    return ( str[ i ] == '\0' ) ? n : 0;
}
void itob( int n , char * string , int b ){
    int i , r;
    for( i = 0;n > 0; ++i ){
        string[ i ] = ( r = n % b ) ;
        n /= b;
    }
    string[ i ] = '\0';
    reverse( string );
    return;
}
void reverse( char * s ){    // taken from K&R, pg 63.
    int c , i , j;
    for( i = 0 , j = strlen( s ) - 1; i < j; ++i , --j )
        c = s[ i ] , s[ i ] = s[ j ] , s[ j ] = c;
    return;
}
char * find_space( int n , int b ){
    int i;
    char * string;
    for( i = 1;n > 0;++i )        // EDIT: changed i = 0    to    i = 1 , counting , not using array indexing
        n /= b;
    string = malloc( ( sizeof( char ) * i ) + 1 );
    return string;
}

---

EDIT: I know i dont free my malloc string, not worried about that right now :)

What input are you giving it? I assume it's something that ends in zero in your new base, e.g. 32 in base 10 becomes 20 in base 16. Your problem is on line 45, you are assigning the numeric value, not the ASCII value to string[i]. That means you put a zero (null character) in string[0], instead of an ASCII '0'.

Ahhhh yes, thank you very much Andreas!

Code:

---

...
for( i = 0;n > 0; ++i ){
        r = ( n % b ) + '0' , string[ i ] = r;
        n /= b;
    }
    string[ i ] = '\0';

---

It's anduril, not Andreas, but no biggie.

One other thing, why do you make such heavy use of the comma? You can use it in a for loop if you have two things to initialize or increment. Outside of that, and the obvious function parameter, you should use it sparingly. Put statements on their own line and use a semicolon to separate them. Avoid cramming too much stuff into one line/statement in general. It makes your code much easier to read (i.e. you'll make fewer bugs, and it will be easier for you and us to find and fix them).