字符串面试题：将字符串转换为整数

在上一篇博文中介绍了如何实现将整数转换为字符串，这里在介绍一个将字符串转换为整数的实现方法。

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

int isspace(int x);
int isspace(int x);
int my_atoi(const char *nptr);

int main(void)
{
    char str[33];
    int  num;
    scanf("%s", str);
    num = my_atoi(str);
    printf("Ans: %d
", num);

    return 0;
}

int isspace(int x)
{
    if(x==' ' || x=='	' || x=='
' || x=='f' || x=='' || x=='
')
        return 1;
    else  
        return 0;
}

int isdigit(int x)
{
    if(x<='9' && x>='0')         
        return 1; 
    else 
        return 0;
}

int my_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;

    // 读取第一个非空白符
    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 */
}