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Introduction to Programming

Introduction to Programming. Algorithms. Andreas Savva. What is an algorithm?. An Algorithm is a detailed sequence of simple steps that are needed to solve a problem. It is a step-by-step solution to a problem. Mathematical Example.

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Introduction to Programming

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  1. Introduction toProgramming Algorithms Andreas Savva

  2. What is an algorithm? • An Algorithm is a detailed sequence of simple steps that are needed to solve a problem. • It is a step-by-step solution to a problem.

  3. Mathematical Example • Problem: What is the value ofxin the following equation? 5x – 10 = 30 • Algorithm (Solution): Step 1: 5x = 30 + 10 Step 2:5x = 40 Step 3:x = 40/5 Step 4:x = 8

  4. Making a cake • Step 1:Preheat oven to 200 degrees. • Step 2:Mix the eggs with the sugar. • Step 3: Add the butter, flour, and the rest of the ingredients. • Step 4: Stir for 5 minutes. • Step 5:Put the mixture into a baking pan and cook it in a 175 degrees for 40 minutes. • Step 6:Keep it in the pan for 15 minutes to cool down. • Step7:Serve with vanilla ice-cream.

  5. Algorithms Algorithm Step 1:Move 3 squares and turn right. Step2:Move 1 square and turn left. Step3:Move 2 squares and turn left. Step4:Move 2 squares and turn right. etc. The Problem: How will the robot go to the file folder?

  6. Representation of Algorithms • Verbal representation • Pseudo-code • Flowchart

  7. Verbal representation of Algorithms • Example:Write an algorithm to read and calculate the average of three numbers. • Algorithm: Step 1:Ask for the first number. Step 2:Ask for the second number. Step 3:Ask for the third number. Step 4:Add the three numbers to find their sum. Step 5:Divide the sum by 3. Step 6:Display the result.

  8. Flowcharts- graphical representation of an algorithm Start – Finish Flow Input – Output Processing Sub-programs (Separate flowchart) Choice Statements (Question, Decision) Comments

  9. G R Sum Average a b c Start Flowchart Read a Read b Read c Sum  a + b + c Average  Sum / 3 DisplayAverage Finish

  10. Structures • For the solution of a problem we use three basic structures: • Sequential structure • Conditional structure • Repetitive structure

  11. Example 2 • Write an algorithm to read two numbers and display the appropriate message if the two numbers are equal or not. • Read a. • Read b. • Ifa = b then display that the two numbers are equal. • Else display that the two numbers are NOT equal.

  12. Start Conditional Structure Read a Read b a = b ? FALSE TRUE Display: ”The two numbers are not equal” Display: ”The two numbers are equal” Finish

  13. Example3 • Write an algorithm to read two numbers a and b and find the sum of all the numbers between a and b inclusive. i.e. • a = 3, b = 7, Sum = 3 + 4 + 5 + 6 + 7 = 25 • a = 1, b = 100, Sum = 1 + 2 + 3 + … + 100 = 5,050 • Read a, b • Sum  0 • Counter  a • IfCounter > b then Goto 8 • Sum  Sum + Counter • Counter  Counter + 1 • Goto 4 • Display Sum

  14. i is the Counter Start Repetitive Structure Read a, b Sum  0 i  a i>b ? TRUE FALSE Sum  Sum + i i  i + 1 Display Sum Finish

  15. Exercises • Design a flowchart for the following problems: • Calculate the weekly salary of an employee, when the employee-name, working-hours, and rate-per-hour are given. If the working-hours exceed 40, the rate-per-hour is double than the normal hour. • Given 4 numbers X1, X2, X3, and X4, find and display the smaller one. • Given two numbers A and B. Calculate and display the remainder of their division B:A. (Hind: Keep subtracting A from B until you find a smaller number than A. i.e. for the division 20:6 it will be 20 – 6 = 14; 14 – 6 = 8; 8 – 6 = 2; so Remainder = 2).

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