C :

#include <stdio.h>
#include <ctype.h>
int main(){
    int m,n,i,j;
    char s[101];
    scanf("%d%*c",&n);
    while(n--){
        i=0;
        gets(s);
        while(s[i]){
            if(s[i]<='Z') s[i] = tolower(s[i]);
            else s[i] = toupper(s[i]);
            i++;
        }
        puts(s);
    }
    return 0;
}

C++ :

#include<iostream>
#include<string>
#include<cctype>
using namespace std;
int main(){
	int n;
	cin>>n;
	while(n--){
		string s;
		cin>>s;
		for(string::size_type ix=0;ix<s.size();ix++){
			if(s[ix]>='A'&& s[ix]<='Z')
				s[ix]=tolower(s[ix]);
			else
				s[ix]=toupper(s[ix]);
		}
		for(string::size_type i=0;i<s.size();i++)
			cout<<s[i];
		cout<<endl;
	}
}

Java :

import java.util.Scanner;
public class Main {
	public static void main(String[] args) {
		Scanner sc=new Scanner(System.in);
		int m=sc.nextInt();
		while(m-->0){
			String str=sc.next();
			char c[]=str.toCharArray();
			for(int i=0;i<c.length;i++){
				if(Character.isLowerCase(c[i])){
					System.out.print(Character.toUpperCase(c[i]));
				}else if(Character.isUpperCase(c[i])){
					System.out.print(Character.toLowerCase(c[i]));
				}
			}
			System.out.println();
		}
		sc.close();
	}
}

Python :

# coding=utf-8
b=int(input())
for i in range(0,b,1):
    a=input()
    print( a.swapcase() )