CBSE Class 10 Computer Science Algorithms and Flowcharts Notes Set 01

Algorithm

An algorithm is a finite sequence of clear, logical steps to carry out a task such as solving a problem. A good algorithm is definite (each step is unambiguous), ends after a finite number of steps and is general enough to work for every valid input. Computers cannot reason by themselves, so a problem must be broken into such steps before a program is written in a language like C++ or BASIC.
Example: algorithm to add two numbers. Step 1: read A and B. Step 2: find C = A + B. Step 3: print C. Step 4: stop.
Example: largest of three numbers A, B, C. Step 1: read A, B, C. Step 2: if A > B go to step 3, else go to step 4. Step 3: if A > C let G = A and go to step 6. Step 4: if B > C let G = B and go to step 6. Step 5: let G = C. Step 6: print G. Step 7: stop.

Flowchart

A flowchart is a picture of an algorithm made of boxes joined by arrows that show the order of steps. It helps to find the inputs needed, to check that every input is available and to write an error-free program. The standard symbols are:

1. Terminal (rounded box): start or end.
2. Process (rectangle): calculation or assignment.
3. Input/output (parallelogram): reading data or printing results.
4. Decision (diamond): a Yes/No question that selects one of two paths.
5. Connector (circle): continues the chart at another place or page.

Example Flowchart

Flowchart to print the larger of two numbers A and B:

Rules for drawing: flow from top to bottom, every box has one entry (a decision has two exits), use arrows on all lines and keep the chart simple. A loop is drawn by taking an arrow back to a decision box so that a set of steps repeats until a condition fails.