// prog 5 - reduce a stack to get prefix expr
#define ME "instructor"

// reduce the expression on top of the stack to prefix form
void reduce (mstr_stack & S) {
mstring op, oprnd1, oprnd2, prefix;
// get 'infix' off stack 
oprnd2=S.pop();
op=S.pop();
oprnd1=S.pop();
//cout << " in reduce" << endl;
//cout << " reducing: " << A << " " << B << " " << C << endl;
// create prefix
prefix=op;
prefix.concatenate(oprnd1);
prefix.concatenate(oprnd2);
// put prefix on the stack
S.push(prefix);
//cout << " out reduce" << endl;
}