Homework # 6 - due Tuesday October 4th

1. Read the section on pre and post conditions and do problems 19 a and b and 20 a from Chapter 3 found on pages 172 & 173 (also shown below)

19. Compute the weakest precondition for each of the following statements and postconditions

a. a = 2 * (b – 1) – 1 {a > 0}

2*(b-1)-1 > 0

2b – 2 -1 > 0

2b – 3 > 0

2b > 3

b > 3/2 Ü required answer (derivation is optional)

b. b = (c + 10) / 3 { b > 6}

(c+10)/3 > 6

(c+10) > 18

c > 8 Ü required answer (derivation is optional)

20. Compute the weakest precondition for each of the following sequences of assignment statements and their postconditions

a. a = 2 * b + 1;

b = a – 3

{ b < 0}

a – 3 < 0

a < 3 Ü required answer (derivation is optional)

1. Answer the Pascal questions found here