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- 1. CSC 103 Lecture 6 Introduction to Computers and Programming
- 2. Pseudo-code and Flow Charts There are two commonly used tools to help to document program logic (the algorithm) These are: Flowcharts Graphical representation used for small problems Pseudo-code English and programming combination used for large problems 2
- 3. Pseudo-code Pseudo-Code is a numbered list of instructions to perform some task Statements are written in simple English without regard to the final programming language Each instruction is written on a separate line The pseudo-code is the program-like statements written for human readers, not for computers Implementation is to translate the pseudo-code into programs, such as “C” language programs 3
- 4. Writing Pseudo-code Number each instruction This is to enforce the notion of an ordered sequence of operations Furthermore we introduce a dot notation (e.g. 3.1 come after 3 but before 4) to number subordinate operations for conditional and iterative operations Each instruction should be unambiguous and effective Completeness: Nothing is left out 4
- 5. Basic Elements of Pseudo-code A Variable Having name and value There are two operations performed on a variable Assignment Operation is the one in which we associate a value to a variable. The other operation is the one in which at any given time we intend to retrieve the value previously assigned to that variable (Read Operation) 5
- 6. Basic Operations of Pseudo-code Assignment Operation This operation associates a value to a variable. While writing Pseudo-code you may follow your own syntax. Some of the possible syntaxes are: Assign 3 to x Set x equal to 3 x=3 6
- 7. Basic Operations of Pseudo-code Read Operation In this operation we intend to retrieve the value previously assigned to that variable. For example: Set Value of x equal to y Read the input from user This operation causes the algorithm to get the value of a variable from the user. Get x Get a, b, c 7
- 8. Basic Operations of Pseudo-code Print the output to the user Print x (This will print value of variable x) Print “Your mileage is” x Carry out basic arithmetic computations Set x to 10 Set y to x*x/3 8
- 9. Example: Pseudo-code of calculating area of circle 1. Begin 2. Input value for radius 3. Calculate area (pi x radius2 ) 4. Output radius and area 5. Quit THEN PROGRAM 9
- 10. Flow Chart Graphical representation of an algorithm Some of the common symbols used in flowcharts are shown: Start/Stop Preparation Input/Output Process Decision Connector 10
- 11. With flowcharting, essential steps of an algorithm are shown using the shapes above. The flow of data between steps is indicated by arrows, or flowlines. For example, a flowchart (and equivalent Pseudocode) to compute the interest on a loan is shown below: 11
- 12. Pseudo-codeFlow chart 1. Read NAME, BALANCE, RATE 2. Compute INTEREST as BALANCE x RATE 3. Write (Display) NAME and INTEREST Stop Start Read NAME, BALANCE, RATE INTEREST=BALANCE x RATE Write NAME, INTEREST 12
- 13. Note that the Pseudo-code also describes the essential steps to be taken, but without the graphical enhancements. Another example of a flowchart and the equivalent pseudo-code is shown next. 13
- 14. Pseudo-codeFlow chart 1. Read X,Y,Z 2. Compute Sum(S) as X+Y+Z 3. Compute Average(A) as S/3 4. Compute Product(P) as X x Y x Z 5. Write (Display) Sum, Average and Product Stop Start Read X, Y and Z S= X+Y+Z A = S/3 P = X x Y x Z Write S, A and P 14
- 15. Some Examples Write pseudo-code of a program that asks the user to enter two numbers and prints the sum, product, difference, and division of the two numbers. Write pseudo-code of a program that solves a quadratic equation ax2+bx+c by taking a, b and c as input from user. 15
- 16. Decision Making and Pseudo-code 16
- 17. Stop Start Read A, B BIG = A SMALL = B Write BIG, SMALL BIG = B SMALL = A A < B ? YesNo 1. Read A, B 2. If A is less than B 2.1 BIG = B 2.2 SMALL = A 3. Else 3.1 BIG = A 3.2 SMALL = B 4. Write BIG, SMALL Example 17
- 18. Loops and Pseudo-code 18
- 19. Start K=1 K=K+1 K > 10? Procedure Stop Yes No 19
- 20. Draw the Flowchart 1. get hours worked 2. get pay rate 3. if hours worked ≤ 40 then 3.1 gross pay = pay rate times hours worked 4. else 4.1 gross pay = pay rate times 40 plus 1.5 times pay rate times (hours worked minus 40) 5. display gross pay 6. End 20
- 21. Draw the Flowchart 1. get number of quizzes 2. sum = 0 3. count = 0 4. while count < number of quizzes 4.1 get quiz grade 4.2 sum = sum + quiz grade 4.3 count = count + 1 5. average = sum / number of quizzes 6. display average 7. End 21

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