Question

2. Trace the following algorithm and determine the return value: Name : Algorithm AB Input : None Output: An integer 1 a = 0 2 b = 20 3 while a < b : 4 a = a + 1 5 b = b - 2 6 end while 7 return a - b

Answer 1

1 a=0

2 b=20

3 while a<b

4      a=a+1

5    b=b-2

6 end while

7 return a-b

Trace:

Initially

a=0

b=20

1st iteration

while(a<b) (0<20 which is true )

a=a+1 =0+1=1

b=b-2=20-2=18

2nd iteration

while(a<b) (1<18 which is true )

a=a+1 =1+1=2

b=b-2=18-2=16

3rd iteration

while(a<b) (2<16 which is true )

a=a+1 =2+1=3

b=b-2=16-2=14

4th iteration

while(a<b) (3<14 which is true )

a=a+1 =3+1=4

b=b-2=14-2=12

5th iteration

while(a<b) (4<12 which is true )

a=a+1 =4+1=5

b=b-2=12-2=10

6th iteration

while(a<b) (5<10 which is true )

a=a+1 =5+1=6

b=b-2=10-2=8

7th iteration

while(a<b) (6<8 which is true )

a=a+1 =6+1=7

b=b-2=8-2=6

8th iteration

while(a<b) (7<6 which is false loop fails)

end while loop

return a-b (7-6=1)

there fore output =1