C code 字符串与整数的相互转化

#include<stdio.h>
int str_to_int(const char *str,int *num);
void int_to_str(char str[],const int strLen,const int num);

int main(int argc,char *argv[])
{
    char str[16];
    int ret = 0,n = 0;
    while(1)
    {
        scanf("%s",str);
        ret = str_to_int(str,&n);
        if(ret == 0)
        {
            printf("%d
",n);
            int_to_str(str,16,n);
            printf("%s
",str);
        }
        else
        {
            printf("error
");
        }
    }
    return 0;
}

int str_to_int(const char *str,int *num)
{
    int sign = 1;
    *num = 0;
    const char *p = str;
    while(*p != '')
    {
        if( *p >= '0' && *p <= '9' )
        {
            *num = *num * 10 + *p - '0';
            p++;
        }
        else if( *p == '-' && *num == 0)
        {
            sign = -1;
            p++;
        }
        else
        {
            return -1;
        }
    }
    *num *= sign;
    return 0;
}

void int_to_str(char str[],const int strLen,const int num)
{
    int tmp = 0,n = 0,i = 0;
    if(num < 0)
    {
        n = -num;
        i = 1;
    }
    while(n != 0)
    {
        tmp = tmp * 10 + n%10;
        n /= 10;
    }
    while(i<strLen && tmp != 0)
    {
        str[i++] = tmp % 10 + '0';
        tmp /= 10;
    }
}