did i understand it right?

i can not pass a variable to a function like this:

function test(a)
{
if(a==0){exit;}
}

test(0);

you have to do it that way?:

function test(&a)
{
if(a==0){exit;}
}

test(0);

or is this jsut with vectors and normal variables are working?
i am often having problems with parameters .,.
like when the number is 0, it crashs..and something like that.. >,<