Lab 2 CSIT-120 Fall 2000

1. Lab 2 CSIT-120 Fall 2000 • Session II-A (September 14th) • Operations on Data • Lab Exercise 2-A • Data Types • Variables • Lab Exercise 2-B • Session II-B (September 21st) (starts on slide 24)

2. Lab-1 Revision • When closing a program and starting to write a new program, what should we do? • What symbols should precede comments? • What is in a header file? • If there is only one function in your program, what is its name? • What does “cout” statement accomplish?

3. Operations on Data • C++ can work with many types of data • Programs need to do “number crunching” if these are to be of any use • In previous labs we have seen how C++ can use I/O functions to output text strings • In a similar way Programs and functions can also handle numbers

4. Lab Exercise 2-A • Perform Experiment 2.1 Page 17 of the lab manual

5. Operations on Data • We have seen that the computer has an ALU that can perform a lot of operations on the data • We can develop programs in C++ that use these ALU operations for solving our real life problems • In order to do so, we need to follow C++ syntax and common sense rules

6. Some Rules to Know • To do effective programming for problem solving, we should state the problem to be solved as clearly as possible. • The problem statement is sufficient to determine the data requirements • Also, it can be used to develop an algorithm for solving it on the computer

7. An Example • As an example, consider following problem • A customer deposits checks in his/her bank account as follows: • check #1: $435.61 • check #2: $365.89 • and at the same time withdraws 200 dollars cash. Can you write a computer program that displays the credit and debit separately for this transaction and then display final amount of money credited into the account?

8. Statement Analysis • We can quickly determine the data requirements of the program by highlighting the nouns used in the statement • Mini Exercise2-1: Determine the data requirements of the program • We can also determine if data items are input or output

9. Algorithm Development • Once we know the data items, we can analyze the question(s) posed in the problem statement • Thus we can start developing an algorithm to solve the problem • Mini Exercise2-2: Analyze the problem and develop the steps required to solve it

10. Algorithm Development • The problem is to determine debit and credit separately and then final credit for a transaction for one bank account • It can be solved by using two temporary variables “debit” and “credit” • credit = check1+check2 • debit = withdrawal • final credit = credit - debit

11. Data Types • Once we have determined the data requirements and the algorithm to solve our problem, we need some data formats in order to model our data • For example, the checks submitted were not in whole number amount. We need a format in which we can represent numbers consisting of integer and fractional parts

12. Data Types • Visual C++ provides several data formats (data types) for our programs • Using these data types, we can represent our data in the programs • For example, the amounts • check #1: $435.61 and check #2: $365.89 • can be represented as floating point numbers in a C++ program

13. Data Types • Similarly, the amount of withdrawal ($200) is a whole number. It can be represented as an integer • The integer and floating point numbers can be defined as constants or variables in a program

14. Variables • A constant never changes its value throughout the program • A variable will change its value during the program because the program may assign it some new value after computations • Mini-Exercise2-3 • What are the constants and variables in the data in our example?

15. Data Types and Variables • You have to declare all variables and constants in your program before you use the same • Your program consists of functions like main() etc. • Each function consists of two sections • Declarations and Statements

16. Data Types and Variables • Declarations consist of all constants and variables that you will use in your program • Statements include all the “number crunching” directives that you want the computer to execute • Let us look at the primitive data types in C++ and rules for declaring constants and variables

17. Data Types and Variables • float data type is used to represent numbers that consist of integer and fractional parts. • For example: • CGPA = 2.54 • integer data type is used to represent whole numbers, such as • Number of students = 5000

18. Data Types and Variables • char data type can represent individual characters such as ‘c’ or digits such as ‘9’ • bool data type can be used to determine the result of a test • For example, if signal==RED then don’t_go • Result = (CGPA<2) • if Result==TRUE then performance is poor

19. Data Types and Variables • For constant values, it is advisable to use names instead of using the value directly • For example, • const int MY_LIMIT=500; • if (price > MY_LIMIT) then don’t_buy=TRUE; • if (don’t_buy) then “exit the shop”

20. Data Types and Variables • The names are more meaningful and make the program easier to read • If the constant is used at several places, we do not have to change the value at all these places. We can just change the declaration • Constants are usually named in CAPITAL LETTERS to distinguish the same from variables

21. Data Types and Variables • Variables are declared in the same way as constants, except that initializing with a value is optional • For example, if you want to make your purchase limit flexible, you can declare it as a variable • int my_limit;

22. Data Types and Variables • The identifiers used to declare constants and variables are subject to certain C++ rules • No spaces within the identifier • Do not begin the identifier with a digit or underscores • Letters, underscores and digits allowed • Keep the length under 31 to avoid portability problems

23. Lab Exercise 2-B • Complete the program that can solve the problem of computing and showing credit, debit and effective credit for a transaction • Use structured programming and put a comment on every declaration as well as major block of statements describing what it is and what it accomplishes

24. Session II-B • Review of Topics and Solving Exercise 2-B • Initializing Variables • Experiments • Mod and Div Operators • Experiments • Data Input and Output • Experiments • Lab Assignment #2 Due 9/28

25. Review of Topics Covered • What primitive data types are used in C++ to represent numerical values? • During comparisons, the result may be assigned to a variable. What is the data type of such a variable? • Ex: testresult = (smoke_detector ringing) • if (testresult) then someone is smoking OR there is something on fire

26. Review of Topics • Why do we perform data analysis on the given problem? • What information is obtained from data analysis and how is it used in the program? • Describe the structured method for algorithm development • Why does initial algorithm only show WHAT is to be done?

27. Lab Exercise 2-B Solution • A customer deposits checks in his/her bank account as follows: • check #1: $435.61 • check #2: $365.89 • and at the same time withdraws 200 dollars cash. Can you write a computer program that displays the credit and debit for this transaction and display final amount of money credited into the account?

28. Lab Exercise 2-B Solution • First we perform data analysis • We determine that there are : • 3 constant data items check1, check2, withdrawal • 3 output data items credit, debit, effective_credit • All are floating point numbers except withdrawal (whole number)

29. Lab Exercise 2-B Solution • Using data analysis results, we can complete the declarations part of the C++ program • float const CHECK1= 435.61; • float const CHECK2= 365.89; • int const WDRAW=200; • float credit,debit,effective_credit;

30. Lab Exercise 2-B Solution • Next, we develop an algorithm to solve this problem INITIAL • Read the check amounts and withdrawal amount • Determine credit, debit and effective credit • Display results and Exit

31. Lab Exercise 2-B Solution • Final Algorithm is obtained by refining initial algorithm FINAL • Read the check amounts and withdrawal amount • {check1, check2, withdrawal initialized as constants} • Determine credit, debit and effective credit • {credit=check1+check2; debit=withdrawal and effective credit=credit-debit;} • Display results and exit • {display credit, debit and effective credit}

32. Initializing Variables • We initialize variables before trying to use the same on RHS of a computation or printing out their values • Experiment 2.4 lab manual • Reading from the user • Let us demonstrate how to read something from the user and display it back

33. Mod and Div Operators • You can perform all arithmetic operations on numeric data including division • Division can be done in two ways • Div operator (/) performs integer division on two integer arguments, truncating remainder • Mod (%) operator results in remainder after the division has been carried out

34. Mod and Div Operators • Perform Experiment 2.6 (Demo Required) • Lab Assignment 2(Due 9/28/2000) • Write a C++ program to convert a given amount into quarters, dimes, nickles and pennies (Hint: convert to cents first and write an algorithm for doing it by hand). Your program should accept the amount from the user using cin>>amount; and finally it should print the number of all coin denominations