FINDING THE CASE OF THE GIVEN INPUT

 main()
{
int input_char;
printf("\n Enter character:");
input_char=getchar();
if(input_char==EOF)
{
printf("End of file encountered \n");
}
else if(input_char>='a'&& input_char<='z')
{
printf("Lowercase character\n");
}
else if(input_char>='A'&& input_char<='Z')
{
printf("uppercase character \n");
}
else if(input_char>=0 && input_char<=9)
{
printf("Digit \n");
}
}

FINDING LEAP YEAR, SWAP OF TWO NUMBERS WITHOUT TEMP VARIABLE

The program which displays the string which you given as input

main()
{
char line[80];
clrscr();
printf("Enter the phrase:");
scanf("%[ABCDEFGHIJKLMNOPQRSTUVWXYZ]",line);
scanf("%[abcdefghijklmnopqrstuvwxyz]",line);
printf("\n The phrase you had typed in was :%s",line);
getch();
} 
o/p
Enter the phrase:hello
The phrase you had typed in was:hello 

The program to find leap year

main()
{
int month,day,year, feb_max;
clrscr();
printf("\n Enter month and year:");
scanf("%d%d",&month,&year);
if(month==2)
{
printf("\n Month is February");
feb_max=28;
if((year%4)==0)
{
printf("\n Leap year");
feb_max=29;
}
printf("\n Max days in this month:%d", feb_max);
}
getch();
}

How the pre-increment and post-increment works

main()
{
int i;
clrscr();
i=3;
printf("i=%d\n",i);
printf("i=%d\n",++i);
printf("i=%d\n",i);
printf("i=%d\n",i++);
printf("i=%d\n",i);
getch();
}
o/p
i=3
i=4
i=4
i=4
i=5

Swap of two numbers without temp variable

main()
{
int a,b;
clrscr();
a=5;
b=10;
a=a+b;
b=a-b;
a=a-b;
printf("%d\n%d\n",a,b);
getch();
}

CHANGING UPPERCASE CHARACTER TO LOWERCASE CHARACTER

program displays a character entered in the uppercase in the lowercase

main()

{

int c;

printf("Enter an uppercase letter:");

c=getchar();

printf("Lowercase=");

putchar(c+32);

}

HOW TO DENOTE END OF FILE

How CTRL+Z can be used to denote end of file:
main()
{
int c;
print("Enter the character (CTRL+Z to end):");
c=getchar();
if(c!=EOF)
printf("End of file not encountered ");
} 
o/p:
Enter the character (CTRL+Z to end):d
End of file not encountered.