Week 2L - Computer Algorithms (1).pptx

Computer Algorithms (COS 101) Week 2 Dr. Desmond Moru [email protected] What is an Algorithm? 2  Other Definitions 1 A finite set of unambiguous instructions performed in a prescribed sequence to achieve a goal, especially a mathematical rule or procedure used...

Computer Algorithms (COS 101) Week 2 Dr. Desmond Moru [email protected] What is an Algorithm? 2  Other Definitions 1 A finite set of unambiguous instructions performed in a prescribed sequence to achieve a goal, especially a mathematical rule or procedure used to compute a desired result. 2 A predetermined set of instructions for solving a specific problem in a limited number of steps. 3 A precise step-by-step plan for a computational procedure that possibly begins with an input value and yields an output value in a finite number of steps. 3  Why do we need an Algorithm? You use a computer algorithm to prepare a roadmap of the program to be written, before actually writing the 1 code. Algorithmic thinking, or the ability to define clear steps to solve a problem, is crucial in many different fields. Even if we’re not conscious of it, we use algorithms and algorithmic thinking all 2 the time. Algorithmic thinking allows you to break down problems and conceptualize solutions in terms of discrete steps. 3 Being able to understand and implement an algorithm requires you to practice structured thinking and 4 reasoning abilities. 4 Characteristics of a Good Algorithm Precision: The steps are precisely stated or defined. Uniqueness: Results of each step are uniquely defined and only depend on the input and the result of the preceding steps. Finiteness: The algorithm always stops after a finite number of steps. Input: The algorithm receives some input. Output: The algorithm produces some output. 5 Advantages of Algorithm It is a step wise representation of a solution to a given problem, which makes it easier to understand. An algorithm uses a definite procedure. It is not dependent on any programming language, so it is easy to understand for anyone without programming knowledge. Every step has its on logical sequence, so it is easy to debug By using algorithm, the problem is broken down into smaller pieces or steps hence, it is easier for programmer to convert it into an actual program. 6  Components of an Algorithm The output desired by the user. Process Processing or computation to be performed to get Input the desired result. The input to be taken from the user. 7 Disadvantages of Algorithm Algorithms is time consuming. Complex problems cannot be solved. Small solutions are not clearly shown. Requires lots of data. Difficult to show branching and looping in algorithms. Big tasks are difficult to put in algorithms. Low performance. 8 Benefits of Algorithms In computers, an algorithm is very important when we want a specific set of instructions for performing a specific task that is definite. It works well in automated and high-frequency trending systems. Algorithms make people’s lives easier because they save slots of time for the things that are time taking if done manually. In an algorithm the problem is divided into parts then it becomes easy to understand every level of the process with logic. 9  Representation of Algorithms There are two common methods of representing an algorithm: Flowcharts Pseudocodes 10 Flowchart — Visual Representation of Algorithms A flowchart is a diagram made up of boxes, diamonds and other shapes, connected by arrows. Each shape represents a step of the solution process and the arrow represents the order or link among the steps. 11 Flowchart — Visual Representation of Algorithms 12  Flowchart — Visual Representation of Algorithms Algorithm to find square of a Start number Input num square = num * num Print square Stop 13  Flowchart — Visual Representation of Algorithms Check bulb Start switch Is the bulb N Switch On switch on? A flowchart to solve the Y problem of a non- N Call Electrician Bulb On? functioning light bulb Is it Burnt N Y Out? Y Replace the Bulb Leave Stop bulb On 14  Pseudocode A pseudocode is another way of representing an algorithm. It is considered as a non-formal language that helps programmers to write algorithm. It is a detailed description of instructions that a computer must follow in a particular order. It is intended for human reading and cannot be executed directly by the computer. No specific standard for writing a pseudocode exists. 15  Pseudocode Example Write an algorithm to calculate area and perimeter of a rectangle, using both pseudocode and flowchart. Pseudocode for calculating area and perimeter of a rectangle INPUT length INPUT breadth COMPUTE Area = length * breadth PRINT Area COMPUTE Perim = 2 * (length + breadth) PRINT Perim 16  Pseudocode Some of the frequently used keywords while writing pseudocode: INPUT COMPUTE PRINT INCREMENT DECREMENT IF/ELSE WHILE TRUE/FALSE 17 The Flowchart Start Input length, breadth Area = length * breadth Print Area Perim = 2 * (length + breadth) Print Perim Stop 18 Benefits of Pseudocode Pseudocode helps in representing the basic functionality of the intended program. By writing the code first in a human readable language, the programmer safeguards against leaving out any important step. For non-programmers, actual programs are difficult to read and understand, but pseudocode helps them to review the steps to confirm that the proposed implementation is going to achieve the desire output. 19