C :

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

int main()
{
	int n,i,j;
	char a[50],b[50],c[100];
	scanf("%d",&n);
	while(n--)
	{
		scanf("%s%s",a,b);
		for(i=0;i<strlen(a)/2;i++)
			c[i]=a[i];
		for(i=strlen(a)/2,j=0;j<strlen(b);i++,j++)
			c[i]=b[j];
		for(j=strlen(a)/2;a[j]!='\0';i++,j++)
			c[i]=a[j];
		c[i]='\0';
		printf("%s\n",c);
	}
	return 0;
}

C++ :

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

int main()
{
	int n,i,j;
	char a[50],b[50],c[100];
	scanf("%d",&n);
	while(n--)
	{
		scanf("%s%s",a,b);
		for(i=0;i<strlen(a)/2;i++)
			c[i]=a[i];
		for(i=strlen(a)/2,j=0;j<strlen(b);i++,j++)
			c[i]=b[j];
		for(j=strlen(a)/2;a[j]!='\0';i++,j++)
			c[i]=a[j];
		c[i]='\0';
		printf("%s\n",c);
	}
	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){
			StringBuffer sb = new StringBuffer(in.next());
			sb.insert(sb.length()/2, in.next());
			System.out.println(sb);
		}
	}

}