How can we access the vdu memory through a c program without using functions.?

i saw one question that to write a program for changing capital letter to small and small to capital by using vdu memory but it should stop the moment when user hits a key from the keyboard. i tried but it is not executing. this question is from LET US C book at 255 pg.no.

How can we access the vdu memory through a c program without using functions.?
This program changes the capital letter to small and vice versa but only if


there is a 'character'. so first type something to command prompt, dont use


clrscr() in the program after declaration and run it.





otherwise





try following

















#include%26lt;stdio.h%26gt;


#include%26lt;conio.h%26gt;


void main()


{


int a,b,i,r,c,ch;


char z='a';


char far *s;


clrscr();





for(a=0;a%26lt;24;a++)


for(b=0;b%26lt;79;b++)


printf("%c",z); //for filling the screen.





while(!kbhit())


{


for(r = 0; r%26lt;=24; r++)


{


for(c = 0; c%26lt;=79; c++)


{


s = 0xB8000000 + r*160 + c*2;


if(*s %26gt;= 'A' %26amp;%26amp; *s %26lt;= 'Z')


*s = *s+32;


else


{


if(*s %26gt;= 'a' %26amp;%26amp; *s%26lt;='z')


*s = *s -32;


}


}


}


}


}