C :

#include<stdio.h>
#include<string.h>

int main()
{
	int n,i;
	char a[51],c;
	scanf("%d%*c",&n);
	while(n--)
	{
		gets(a);
		for(i=0;i<strlen(a)-1;i=i+2)
		{
			c=a[i];
			a[i]=a[i+1];
			a[i+1]=c;
		}
		puts(a);
	}
	return 0;
}

Java :

import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		int t = in.nextInt();
		while(t-->0){
			String s = in.next();
			StringBuffer sb = new StringBuffer();
			for(int i=0;i<s.length();i+=2)
				sb.append(s.charAt(i+1)).append(s.charAt(i));
			System.out.println(sb);
		}
	}

}