It is nothing but breaking down problem into smaller and more manageable problems.

It is a diagrammatic representation of algorithms.

Pseudo code is a notation similar to programming languages.

Flowcharts have disadvantages:
(i) Flowcharts are less compact than a representation of algorithms in 132 programming language or pseudo code.
(ii) They obscure the basic hierarchical structure of the algorithms.
(iii) Alternative statements and loops are disciplined control flow structures. Flowcharts do not restrict us to disciplined control flow structures

(i) Pseudo code is a mix of programming-language like constructs and plain English. This notation is not formal nor exact. It uses the same building blocks as programs, such as variables and control flow.
(ii) But it allows the use of natural English for statements and conditions. An algorithm expressed as pseudo code is not for computers to execute directly, but for 'human readers to understand.
(iii) Therefore, there is no need to follow the rules of the grammar of a programming language. However, even pseudo-code must be rigorous and correct. Pseudo code is the most widely used notation to represent algorithms

Decomposition breaks down a problem into smaller subproblems and combines their solutions to solve the original problem.

Programming language, pseudo code, flowchart are notations for expressing algorithms.

(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.

Disadvantages of flowcharts:
1. Flowcharts are less compact than representation of algorithms in programming language or pseudo code.
2. They obscure the basic hierarchical structure of the algorithms.
3: Alternative statements and loops are disciplined control flow structures.

Alternative statement analyses the problem into two cases. Case analysis statement generalizes it to multiple cases. Case analysis splits the problem into an exhaustive set of disjoint cases. For each case, the problem is solved independently. If C1, C2, and C3 are conditions, and S1, S2, S3 and S4 are statements, a 4-case analysis statement has the form,
1. case C1
2. S1
3. case C2
4. S2
5. case C3
6. S3
7. else
8. S4
The conditions C1, C2, and C3 are evaluated in turn. For the first condition that evaluates to true, the corresponding statement is executed, and the case analysis statement ends. If none of the conditions evaluates to true, then the default case S4 is executed.
(i) The cases are exhaustive: at least one of the cases is true. If all conditions are false, the default case is true.
(ii) The cases are disjoint: only one of the cases is true. Though it is possible for more than one condition to be true, the case analysis always executes only one case, the first one that is true. If the three conditions are disjoint, then the four cases are (1) C1, (2) C2, (3) C3, (4) (not C1) and (not C2) and (not C3).