Bai 1:

//name:           bai 1.c

//author:         Vu Duy Hung

//description:    Bai tap 1

#include <stdio.h>

int main()

{

    char x;

    printf("nhap ki tu: ");

    scanf("%c",&x);

    if(x>=65&&x<=90)

    {

                  x=x+32; 

                  printf("chu cai thuong tuong ung%c",x);

                  }

    else

        {

                  if(x>=97&&x<=122)

                  {

                                   x=x-32;

                                   printf("chu cai thuong tuong ung %c",x);

                                   }

                  else

                  {

                      printf("%c khong la chu cai",x);

                      }

        }

    getch ();

    return 0;

    }

bai 2 :

#include <stdio.h>

int main()

{

    int x;

    printf("nhap so:");

    scanf("%d",&x);

    switch (x)

    {

           case 0:printf("chu so khong");break;

           case 1:printf("chu so mot");break;

           case 2:printf("chu so hai");break;

           case 3:printf("chu so ba");break;

           case 4:printf("chu so bon");break;

           case 5:printf("chu so nam");break;

           case 6:printf("chu so sau");break;

           case 7:printf("chu so bay");break;

           case 8:printf("chu so tam");break;

           case 9:printf("chu so chin");break;

           default: system ("pause");

           getch()     

           return 0;

           }     

    getch()

    return 0;

    }