44  Pascal User Manual  You are further cautioned that a carelessly formulated if statement  can be very costly. Take the example where there are n  mutually  exclusive  conditions,  C1 ... Cn,  each instigating a distinct action,  Si.  Let  P (Ci)  be the probability of Ci being true, and say that  P (Ci)  >=  P (C  j)  for  i  <  j. Then the most efficient sequence of if clauses is:  if expression1 then  begin if expression2 then statement1  else statement2  end  if C1  then Sl  else if C2  then S2  else  else if C(n-1)  then S(n-1)  else Sn  The fulfillment of a condition and the execution of its statement  completes the if statement, thereby bypassing the remaining tests.  If  Found  is a variable of type  Boolean,  another frequent abuse of  the if statement can be illustrated by:  if Key  =  ValueSought then Found .- true  else Found := false  A much simpler statement is:  Found := Key = ValueSought  The  following  program  transforms  Arabic  numbers  to  Roman  numerals by successively reducing the number in a sieve implemented  by using if statements.  program ArabicToRoman(Output);  { Program 4.9 - Write a  table of powers of 2  in  Arabic numbers and Roman numerals.  var  Rem  {remainder},  Number:  Integer; 