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CSCI 130

CSCI 130. Pseudocode. Structure Theorem. Any program can be created by using the following 3 control structures: sequence selection (IF-THEN-ELSE) iteration (DOWHILE). What is Pseudocode?. English like statements depicting the flow of logic in a computer program 1. Simple english

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CSCI 130

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  1. CSCI 130 Pseudocode

  2. Structure Theorem • Any program can be created by using the following 3 control structures: • sequence • selection (IF-THEN-ELSE) • iteration (DOWHILE)

  3. What is Pseudocode? • English like statements depicting the flow of logic in a computer program • 1. Simple english • 2. One instruction per line • 3. Keywords and Indentation - clarity • 4. Top to bottom - one entry, one exit • 5. Modules

  4. Key Words • Receive info: READ, GET • Display info: DISPLAY, PUT, OUTPUT • Decision: IF…THEN…ELSE • Iteration: DOWHILE

  5. Sequence Example • Write pseudocode for a program which will input the radius of a circle, and which will output the area

  6. Sequence Solution • GET radius • area = pi * radius * radius • OUTPUT area

  7. Selection 1 Example • Write the pseudocode for a program that will accept a number that is less than 100, and will output the number only if it meets that condition

  8. Selection 1 Solution • GET x • IF x < 100 • OUTPUT x • END IF

  9. Selection 2 Example • Write the pseudocode for a program that will determine the net income given the gross income of an employee. Determine the tax according to the following table: • 0 - 10000 10% • 10001 - 20000 15% • 20001 - 50000 20% • Over 50000 30%

  10. Selection 2 Solution • GET grossIncome; • IF grossIncome < 10001 THEN • netIncome = grossIncome * .1 • ELSE • IF grossIncome < 20001 THEN • netIncome = grossIncome * .15 • ELSE • IF grossIncome < 50001 THEN • netIncome = grossIncome * .2 • ELSE • netIncome = grossIncome * .3 • END IF • END IF • END IF • DISPLAY netIncome

  11. Iteration • Counted DOWHILE • number of iterations is known in advance • DOWHILE • number of iterations is not known in advance • sentinel • end of file

  12. Counted DOWHILE Example • Write the pseudocode for a program which will read in 10 numbers and output the sum and average

  13. Counted DOWHILE solution • totalSum = 0 • average = 0 • DOWHILE counter = 1 to 10 • read num • totalSum = totalSum + num • ENDO • average = totalSum / 10 • OUTPUT totalSum, average

  14. DOWHILE example 1 • Write the pseudocode for a program that will allow the user to input numbers. The signal (sentinel) from the user that they are done is that they will enter 999. The program will then output the sum of the numbers.

  15. DOWHILE solution 1 • total = 0 • READ num • DOWHILE (num not= 999) • total = total + num • READ num • ENDO • OUTPUT total

  16. DOWHILE example 2 • Write the pseudocode for a program that will read in records from a file. The program will extract the first name, last name, and salary from the file. It will then output the first name, last name, and salary of each employee. At the end of the program, the total payroll is output.

  17. DOWHILE solution 2 • totalPayroll = 0 • DOWHILE records exist • READ inputRecord • EXTRACT firstName, lastName, salary • WRITE firstName, lastName, salary • totalPayroll = totalPayroll + salary • ENDO • WRITE totalPayroll

  18. Control Structures can be nested • Decision structures within decision structures • DOWHILES within DOWHILES • Decisions structures within DOWHILES • DOWHILES within Decision structures • etc.

  19. Putting it all together • Write the pseudocode for a program which will accept a number grade as input, and which will output a message stating whether the student passed or failed. In addition, after each grade is done, ask the user if they want to continue. If they answer ‘YES’, request another grade, otherwise end the program.

  20. Solution • answer = ‘YES’ • DOWHILE answer = ‘YES’ • GET grade • IF grade >= 60 • OUTPUT ‘Student Passed’ • ELSE • OUTPUT ‘Student Failed’ • END IF • GET answer • ENDO

  21. Modules • Subtasks • Increases Readability • Easier Development/Maintenance • Program may have Modules (functions, paragraphs) but pseudocode does not necessarily show this (complex functions will be broken out in pseudocode) • Module call matches module name EXACTLY

  22. Module Example • Write the pseudocode for a program that will accept a number in inches, and which will output that number converted to feet and yards

  23. Module Solution • GET inches • ConvertToFeet • ConvertToYards • Modules: • ConvertToFeet • feet = inches / 12 • OUTPUT feet • ConvertToYards • yards = inches / 36 • OUTPUT yards

  24. Module Solution 2 • GET inches • feet = ConvertToFeet(inches) • yards = ConvertToYards(inches) • OUTPUT feet • OUTPUT yards • Modules: • ConvertToFeet(inputInches) • feet = inputInches / 12 • ConvertToYards(inputInches) • yards = inputInches / 36

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