C :

#include <stdio.h>

int main()
{
	char c[100];
	gets(c);
	int i;
	for (i=0;i<100;i++)
	{
		if (c[i]>='A' && c[i]<='Z')
		{
			c[i]= 'A' + 26- (c[i]-'A'+1);
		}
		if (c[i]>='a' && c[i]<='z')
		{
			c[i]= 'a' + 26- (c[i]-'a'+1);
		}
	}
	printf ("%s\n",c);
	return 0;
}

C++ :

#include<stdio.h>
#include<string.h>
int main()
{
  char s[100];
  int i=0;
    scanf("%s",s);
  for(i=0;i<strlen(s);i++)
  {
    if((s[i]>='a')&&(s[i]<='z'))
      s[i]=219-s[i];
    if((s[i]>='A')&&(s[i]<='Z'))
      s[i]=155-s[i];
  }
  
    printf("%s",s);
  printf("\n");
}

Pascal :

var
s:ansistring;
i:longint;
begin
read(s);
for i:=1 to length(s) do begin
if s[i]='A' then s[i]:='Z';
if ('A'<s[i])and(s[i]<='Z') then s[i]:=chr(ord('A')+26-(ord(s[i])-ord('A')+1));
if s[i]='a' then s[i]:='z';
if ('a'<s[i])and(s[i]<='z') then s[i]:=chr(ord('a')+26-(ord(s[i])-ord('a')+1));
write(s[i]);
end;
end.