atoi和itoa函数的实现

参考：http://c.chinaitlab.com/c/basic/200902/776622.html

 

//atoi的实现

#include<iostream>

using namespace std;

int atio1(char *s)

{

int sign=1,num=0;

    if(*s=='-')

        sign=-1;

    s++;

    while((*s)!='\0')

    {

        num=num*10+(*s-'0');

        s++;

    }   

    return num*sign;   

}

 

 

//itoa的实现

char *itoa(int num, char *str, int radix)
{
    char* ptr = str;
    int i;
    int j;

    while (num)
    {
        *ptr++  = string[num % radix];
        num    /= radix;

        if (num < radix)
        {
            *ptr++  = string[num];
            *ptr    = '\0';
            break;
        }
    }

    j = ptr - str - 1;

    for (i = 0; i < (ptr - str) / 2; i++)
    {
        int temp = str[i];
        str[i]  = str[j];
        str[j--] = temp;
    }

    return str;
}

 

 

 

int main()

{

    char *s="-123567890";   

    cout<<atio1(s);

    system("pause");

}