Second lecture

REGULAR EXPRESSION

Regular Expression

Rules Of Regular Expression (RE)

n* = n0 - ∞

• n0 = ^• n1 = n• n2 = nn• n3 = nnn• | = :• | = :• | = :• n∞ = nnnn……

n+ = n1 - ∞

• n1 = n• n2 = nn• n3 = nnn• | = :• | = :• | = :• n∞ = nnnn……

Note : ^a = a

From (a + b) we can take only a or bie: (a + b)2 = (a + b)(a + b) OR (a + b)2 = (a + b)(a + b)

a b b a

Make bbbabb(a + b)6 (a + b)(a + b) (a + b)(a + b) (a + b)(a + b) 1 2 3 4 5 6 b b b a b b Make abaaa(a + b)5 (a + b)(a + b) (a + b)(a + b) (a + b) 1 2 3 4 5 b b b a b

Make a RE which has all possible character of a & b (a + b)*

1. Write an expression that ends on “b”.2. Write an expression that starts on “b”.3. Write an expression that starts with “a” ends on “b”.4. Write an expression if starts with “a” than ends on “b” and if starts with “b” than ends on “a”.5. Write an expression 2nd word always remain “b”6. Write an expression at least one “a” is occurs

1. (a + b)*b 2. b(a + b)* 3. a(a + b)*b4. a(a + b)*b + b(a + b)*a5. (a + b) b (a + b)*6. (a + b)* a (a + b)*

1. Write an expression involving even numbers of a’s (0a), (2a) aa, (4a) aa aa, (6a) aa aa aa, (8a) aa aa aa aa

2. Write an expression involving odd numbers of a’s (1a) a, (3a) aaa, (5a) aa a aa, (7a) aaa a aaa, (9a) aaa aaa aaa

3. Give only even length of every coming numbers aa, ab, abab, aabb, baab, abbb, abbaab4. Give only odd length of every coming numbers aaa, aba, aaaab, abaab5. User do every thing but answer remain the triple aaa, aba, baa, bab

1. (aa)* 2. a(aa)* 3. [(a + b)(a + b)]*(aa)0 = ^ a(aa)0 = ^a = a 4. [(a + b)(a + b)]*(a + b)(aa)1 = aa a(aa)1 = aaa 5. (a + b) (a + b) (a + b)(aa)2 = aa aa a(aa)2 = aaa aaa(aa)3 = aa aa aa

Assignment No. 1