从键盘输入一个字符如（“12345”只有0-9）用递归算法将字符串转换为数字，

不好意思，之前发的那个没验证发现有点问题，误导了，这个验证了一下没问题。你的题目总没有说明翻译成几进制，所以我就按原样翻译了
例如字符"1234"，翻译为数字1234.

 void GetNumFromString(char *c,unsigned long *num);
void _tmain(int argc, _TCHAR* argv[])
{
    unsigned long x;
    char *pp = "1234";
    x = 0;
    GetNumFromString(pp,(unsigned long *)&x);
    pp = "8234";
    x = 0;
    GetNumFromString(pp,(unsigned long *)&x);
    while(1)
    {

    }
}

void GetNumFromString(char *c,unsigned long *num)
{
    if(*c != '\0')
    {
        *num *= 10;
        if(*c >= '0' && *c <= '9')
            *num += *c - '0';
        GetNumFromString(++c,num);
    }
}

 unsigned long GetNumFromString(char *c)
{
    static unsigned long num = 0;

    if(*c == '\0')
        return num;
    num *= 10;
    if(*c >= '0' && *c <= '9')
        num += *c - '0';
    GetNumFromString(++c);
    return num;
}