i) Specification
ii) Abstraction
iii) Composition
iv) Decomposition

The data stored in a variable is also known as the value of the variable. We can store a value in a variable or change the value of variable, using an assignment statement.

An algorithm is a step by step process to solve the problem.

1. --minimum (a,b)
2. -- inputs: a, b are real numbers.
3. --output: result: minimum (a,b)

An algorithm is a step by step sequence of statements intended to solve a problem. An algorithm starts execution with the input data, executes the statements and finishes execution with the output data.

The order in which the statements are executed may differ from the order in which they are written in the algorithm. This order of execution of statements is known as the control flow.

As the values of the variables are changed, the state changes

(i) Data
(ii) Variables
(ill) Control flow
(iv) Functions.

Assignment statement is used to assign values to the variables.
The variable on the left side of the assignment operator and a value on the right side.
Variable := Value

Specification format: 
We can write the specification in a standard three part format:
(i) The name of the algorithm and the inputs
(ii) Input: the property of the inputs
(iii) Output: the desired input-output relation
The first part is the name of the algorithm and the inputs. The second part is the property of the inputs. It is written as a comment which starts with - inputs: The third part is the desired input-output relation. It is written as a comment which starts with - outputs. \(\therefore \) The input and output can be written using English and mathematical notation.

There are a few basic principles and techniques for designing algorithms.
(i) Specification:
The first step in problem solving is to state the problem precisely. A problem is specified in terms of the input given and the output desired. The specification must also state the properties of the given input, and the relation between the input and the output.
(ii) Abstraction:
A problem can involve a lot of details. Several of these details are unnecessary for solving the problem. Only a few details are essential. Ignoring or hiding unnecessary detail and modeling an entity only by its essential properties is known as abstraction.
(iii) Composition:
An algorithm is composed of assignment and control flow statements. A control flow statement tests a condition of the state and, depending on the value of the condition, decides the next statement to be executed.
(iv) Decomposition:
We divide the main algorithm into functions. We construct each function independently of the main algorithm and other functions. Finally, construct the main algorithm using the functions. When we use the functions. it is enough to know the specification of the function. It is not necessary to know how the function is implemented.

Let the variables a, b, c represent the glass A, glass B and Glass C respectively. Variables A, B, C can store values APPLE, GRAPE or EMPTY.
Initial State:
1.-- a, b, c : = APPLE, GRAPE, EMPTY
2. C : = b
3.-- a, b, c : = APPLE, EMPTY, GRAPE
4. b : = a
5.-- a, b, c : = EMPTY, APPLE, GRAPE
6. a : = C
7.-- a, b, c : = GRAPE, APPLE, EMPTY
Final State:
Specification:
1. Exchange ()
2. -- inputs: a, b, c :- APPLE, GRAPE, EMPTY
3.--outputs: a, b, c:- GRAPE, APPLE, EMPTY