Вывод чисел через одно

#include <iostream>
#include <vector>
#include <string>
#include <iterator>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <cctype>
#include <tuple>
#include <climits>
#include <cstdlib>
#include <unistd.h>
#include <termios.h>
 
char getch(){
    char buf=0;
    struct termios old={0};
    fflush(stdout);
    if(tcgetattr(0, &old)<0)
        perror("tcsetattr()");
    old.c_lflag&=~ICANON;
    old.c_lflag&=~ECHO;
    old.c_cc[VMIN]=1;
    old.c_cc[VTIME]=0;
    if(tcsetattr(0, TCSANOW, &old)<0)
        perror("tcsetattr ICANON");
    if(read(0,&buf,1)<0)
        perror("read()");
    old.c_lflag|=ICANON;
    old.c_lflag|=ECHO;
    if(tcsetattr(0, TCSADRAIN, &old)<0)
        perror ("tcsetattr ~ICANON");
    return buf;
 }
 
int main(int argc, char *argv[])
{
 
    for (char switcher(1), ch = getch(); ch != '\n'; ch = getch())
    {
        if (isdigit(ch) && (switcher = !switcher))
            std::cout << ch;
    }
 
    std::cout << std::endl;
    // [ANTIWARNING] unused parameters: 'argc', 'argv'
    return 0; (void)argc;(void)argv;
}