Algorithm and pseudocode conventions

DATA STRUCTURE AND ALGORITHMS

1. ALGORITHM AND PSEUDOCODE CONVENTIONS BY: SARANYA CHANDRAMOHAN,M.SC.,M.Phil ,

2. ALGORITHM : Algorithm is a step-by-step procedure, which defines a set of instructions to be executed in a certain order to get the desired output.

3. From the data structure point of view, following are some important categories of algorithms Search − Algorithm to search an item in a data structure. Sort − Algorithm to sort items in a certain order. Insert − Algorithm to insert item in a data structure. Update − Algorithm to update an existing item in a data structure. Delete − Algorithm to delete an existing item from a data structure .

4. Characteristics of an Algorithm: Unambiguous − Algorithm should be clear and unambiguous. Each of its steps (or phases), and their inputs/outputs should be clear and must lead to only one meaning. Input − An algorithm should have 0 or more well-defined inputs. Output − An algorithm should have 1 or more well-defined outputs, and should match the desired output. Finiteness − Algorithms must terminate after a finite number of steps. Feasibility − Should be feasible with the available resources.

5. Independent − An algorithm should have step-by-step directions, which should be independent of any programming code . Example: An algorithm to add two numbers and display the result. step 1 − START ADD step 2 − get values of a & b step 3 − c ← a + b step 4 − display c step 5 − STOP

6. Pseudocode : Pseudocode is a notation system for writing algorithms. The pseudocode notation specifies operations that a machine can perform in as human-friendly (e.g., easy to read) way as possible, while avoiding ambiguity.

7. PSEUDOCODE CONVENTIONS: The following conventions must be used to present your pseudo-code 1 . Give a valid name for the pseudo-code procedure. (See sample code for insertion sort at the end) 2 . Use the line numbers for each line of code. 3. Use proper Indentation for every statement in a block structure. 4 . For a flow control statements use if-else. Always end an if statement with an end-if. Both if, else and end-if should be aligned vertically in same line.

8. Ex: If (conditional expression) statements (see the indentation) else statements end-if 5 . Use “=” or “← ” operator for assignment statements. Ex: i = j or I ← j n = 2 to length[A] or n ← 2 to length[A] . 6. Array elements can be represented by specifying the array name followed by the index in square brackets. For example, A[ i ] indicates the ith element of the array A. 7 . For looping or iteration use for or while statements. Always end a for loop with end for and a while with end-while. 8. The conditional expression of for or while can be written as shown in rule (4).

9. Sample pseudo-code for insertion sort using the above conventions: INSERTION-SORT(A ) 1 . for j ← 2 to length[A] 2. key ← A[j] 3. I ← j – 1 4 . while i > 0 and A[ i ] < key // If required, use this convention for a comment 5 . A[i+1] ← A[ i ] // Swap two elements of array. 6 . i ← i –1 7 . end-while 8 . A[i+1] ← key 9 . end-for