1. Enter A,B
2. Initialise Q-0, r-A
3. If r ≥ B, then do Q-Q+1; r-r-B else r,q
4. Exit.

After decomposing a -problem into smaller subproblems, the next step is either to' refine the subproblem or to abstract the subproblem.
1. Each subproblem can be expanded into more detailed steps. Each step can be further expanded to still finer steps, and so on. This is known as refinement.
2. We can also abstract the subproblem. We specify each subproblem by its input property and the input-output relation. While solving the main problem, we only need to know the specification of the subproblems. We do not need to know how the subproblems are solved.

Conditional statement: Sometimes we need to execute a statement only if a condition is true and do nothing if the condition is false. This is equivalent to the alternative statement in which the elseclause is empty. This variant of alternative statement is called a conditional statement. If C is a condition and S is a statement, then
 if      C
    S
is a statement, called a conditional statement, that describes the following action:
1. Test whether C is true or false.
2. If C is true then do S; otherwise do nothing.
The conditional control flow is depicted in the flowchart.

1. compare(a,b)
2. case a
3. result:=-1
4. case a=b
5. result;=0
6. else--a>b
7. result:=1

1. minimum(a,b)
2. --a,b
3. ifa
4. result:=a
5. else
6. result=b
7. --result=a \(\downarrow\) b

(i) Test whether C is true or false.
(ii) If C is true then do S; otherwise do nothing

(1) double (n)
--inputs: n is a real number or an integer, n > 0
--outputs: y is a real number or an integer such that y= n x h.
(2) double (n)
--inputs: n is a real number or an integer, n > 0
--outputs: y is a real number or an integer such that y = 2 x n.

1. Case analysis statement generalizes it to multiple cases.
2. Case analysis splits the problem into an exhaustive set of disjoint cases.

S1; S2; S4