How to replace a stored value?

[altXerror]

i have part of a text based game that keeps track of the HP , DEF... and such. it needs to be able to replace the current value for the variables, in which case are:

long HP, def, sheild;

for instance, you battle a monster and the attack does 75 HP your HP is 100 so:

100-72=25. i need to be able to copy the end result to HP.

how would i do this? do i need to use STRCOPY?

[Caligulaminus]

HP-=75;

[daviddoria]

You may want to take a pass through something like this:
http://www.cplusplus.com/doc/tutorial/

to get an idea of variable types, etc.