An internal implementation method based on atoi of and itoa of functions

The C language provides several standard library functions that convert Numbers of any type (integer, long integer, floating point, etc.) into strings. The following is to use An example of the itoa() function converting an integer toa string:
            atoi         Converts a string to an integer
            itoa         Converts an integer to a string

 #include "stdio.h"
#include "ctype.h"
#include "stdlib.h"

int my_atoi(char s[])
{
 int i,n,sign;
 for(i=0;isspace(s[i]);i++);   //Skip the blank
 sign=(s[i]=='-')?-1:1;
 if(s[i]=='+'||s[i]==' -')     //Skip sign bit
  i++;
 for(n=0;isdigit(s[i]);i++)
  n=10*n+(s[i]-'0');        //Converts numeric characters into plastic Numbers
 return sign*n;
}

void my_itoa(int n,char s[])
{
 int i,j,sign;
 if((sign=n)<0)    //Recording symbols
  n=-n;         //Make n positive
 i=0;
 do{
  s[i++]=n%10+'0';    //Take the next number
 }while((n/=10)>0);      //Cycle division
 if(sign<0)
  s[i++]='-';
 s[i]='0';
 for(j=i-1;j>=0;j--)        //The generated Numbers are in reverse order, so output in reverse order
  printf("%c",s[j]);
}
void main()
{
 int n;
 char str[100];
 my_itoa(-123,str);
 printf("n");
 printf("%dn",my_atoi("123"));
 system("pause");
}