自己实现atoi的功能

整理思路：

#include <stdio.h>
int len(char *s)
{
    int len = 0;
    while (s[len])
    {
        len++;
    }
    return len;
}
int myPower10(int len)
{

    if (len == 0)
        return 1;
    if (len == 1)
        return  10;

    int power = 10;
    for (int i = 1; i < len; i++)
        power *= 10;
    return power;
}
int myCToInt(char c)
{
    c = c - ‘0‘;
    return c;
}

int myAtoi(char *s)
{
    int i, volue = 0,lens = len(s);
    for (i = 0; i < lens; i++)
    {
        volue += myCToInt(s[i]) * myPower10(lens - i - 1);
    }
    return volue;
}

int main()
{
    char a[] = "3321";
    int volue = myAtoi(a);
    printf("%d", volue);
    return 0;
}

运行：

3321