atoi的实现

#include <ctype.h>
#include <stdio.h>

/* atoi: convert s to integer; pointer version */
int atoi(const char *s)
{
    int n, sign;

    for (; isspace(*s); s++);        /* skip white space */

    sign = (*s == '-')? -1 : 1;
    if (*s == '+' || *s == '-')
        s++;
    for (n = 0; isdigit(*s); s++)
        n = n * 10 + (*s - '0');

    return sign * n;
}

int main()
{
    char buff[] = "-1234567890";
    int a;

    a = atoi(buff);
    printf("%d\n", a);

    return 0;
}