AOJ#0002 incorrected

aoj0002.c

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

int itoa(int, char*, const int);
void reverseString(char*);

int main(void)
{
    char buf[100];
    int a, b;

    while(scanf("%d %d", &a, &b))
    {
        printf("%d\n", itoa(a + b, buf, 100));
    }

    return 0;
}

/*
    itoa :: int    -- target
         -> char*  -- string output buffer
         -> int    -- string output buffer size
         -> int    -- string length
*/
int itoa(int num, char* buf, const int limit)
{
    int buflen = 0;
    int nextnum;
    const int lastindex = limit - 1;

    while( num != 0)
    {
        // buffer over flow protection
        if ( buflen < lastindex )
        {
            buflen++; // for put '\0' on last of buffer
            break;
        }

        nextnum = ((num / 10) * 10);
        buf[ buflen++ ] = (char)(num - nextnum);
        num = nextnum;
     }

    buf[ buflen ] = '\0';
    return --buflen;  // string length without '\0'
}


/*
   reverse string
*/
void reverseString(char* string)
{
    const unsigned int length = strlen(string);
    const unsigned int onc = length / 2; // offset nearly center
    unsigned int ofsl, ofsr; // offset from left, offset from right
    char *lp, *rp; // left pointer, right pointer
    int i;

    for ( i = 0; i <= onc; i++)
    {
        ofsl = i;
        ofsr = 1 + i; // be carefuly to '\0'

        lp = string + ofsl;
        rp = string + (length - ofsr);

        // XOR exchange
        *lp ^= *rp;
        *rp ^= *lp;
        *lp ^= *rp;
    }
}