C :

#include <stdio.h>
int main(){
	int i;
	int c1,c2,c3,c4;
	for(i=1000;i<=9999;i++)
	{
		c1=i/1000;
		c2=i%1000/100;
		c3=i%100/10;
		c4=i%10;
		if(c1==c4&&c2==c3)
		printf("%d\n",i);
	}
	return 0;
} 

C++ :

#include <iostream>
#include <cstdio>
#include <cstring>
using namespace std;
int f(char *buf)//判断是否回文串 
{
	for(int i=0; i<strlen(buf)/2; i++)
		if(buf[i]!=buf[strlen(buf)-1-i])
			return 0;
	return 1;
}
int main()
{
	char s[10];
	for(int i=1001;i<=9999;i++)
	{
		sprintf(s,"%d",i);
		if(f(s)) cout<<i<<endl;	
	}
    return 0;
}

Java :

public class Main {
	public static void main(String[] args) {
		for(int i=1000;i<=9999;i++){
			if(i/1000==i%10&&i%1000/100==i%100/10){
				System.out.println(i);
			}
		}
	}
}

Python :

# coding=utf-8
a=[i for i in range(1000,10000)]
for i in a:
    if(str(i)[::-1]==str(i)):
        print(i)