replacing two spaces with an 'x' using only putchar and getchar

This program should replace one space with an x, using only getchar() and putchar(). My approach was to store the space in a buffer and then print it out. But the program replaces every space with an x. Can someone help me out?

#include <stdio.h>
#define MAX 1

char arr[MAX];           
int ret = 0;

int main()                        
{


for(int i=0; ; )      
{
  if ( (ret = getchar())!= EOF)  
  {
       putchar(ret);
  }
  if(ret==' ')
  {
      arr[i]=ret;
      arr[i]='x';
       putchar(arr[i]);
  }





}
return 0;
}