Storing a Value

How do you store/capture a value, such as volume, after an event, such as ALERT, so that you can compare the next value to the last?

int start()
{
int x,k;

static int y;

for (;;)
{
k=1;

x=Volume[0];
Alert ("Minute ",Minute()," Vol ",x," ",y);

y=x;

if (k<10) k++;
}
//----
return(0);
}