atoi实现

isspace(int x){    if(x==' '||x=='/t'||x=='/n'||x=='/f'||x=='/b'||x=='/r')        return 1;    else         return 0;}isdigit(int x){    if(x<='9'&&x>='0')                 return 1;     else         return 0;}int atoi(const char *nptr){        int c;              /* current char */        int total;         /* current total */        int sign;           /* if '-', then negative, otherwise positive */        /* skip whitespace */        while ( isspace((int)(unsigned char)*nptr) )            ++nptr;        c = (int)(unsigned char)*nptr++;        sign = c;           /* save sign indication */        if (c == '-' || c == '+')            c = (int)(unsigned char)*nptr++;    /* skip sign */        total = 0;        while (isdigit(c)) {            total = 10 * total + (c - '0');     /* accumulate digit */            c = (int)(unsigned char)*nptr++;    /* get next char */        }        if (sign == '-')            return -total;        else            return total;   /* return result, negated if necessary */}