1 Lab Session-III CSIT-120 Spring 2001 Revising Previous session Data input and output While loop Exercise Limits and Bounds GOTO SLIDE 13 Lab session III continues (Session III-B)

2 Revising Previous Session Can we use un-initialized variables on RHS of an assignment statement? On LHS? If we are interested in the remainder value from a division, what operator should be used? Can we assign an integer value to a floating point variable?

3 Introducing Loops We have seen in the class the need for a loop structure in searching a list In algorithm development, we can use several types of loops While structure is an example of loops Format: while (condition is true) »execute the statements in loop body

4 Introducing Loops While loop keeps executing statements in the body of the loop until the condition becomes false While (condition 1 is true) do statement1 becomes check condition 1 if true do statement

5 While Conditional Loop We have already looked at the while statement in algorithm development C++ provides the while statement for implementing conditional loops Let us take the vending machine problem in order to develop a program using while loop

6 Vending Machine Algorithm Algorithm begins when the user inserts card Initialize the balance on card with $5 Take the item price from the user While (price of item is less than or equal to amount on card) AND (price entered is not zero) [subtract price from card balance take another item price from the user] Let us implement this algorithm in a C++ program

7 Lab Exercise 3-A (Demo Required) A user is prompted to enter a character. The programs keep reading the characters entered and keeps counting the same. As soon as the user enters ‘q’, the program exits showing the total number of characters entered

8 Assumptions The program will accept a character input from the user It should count the characters entered It should exit on receiving a ‘q’ from the user, displaying total count Let us perform the data analysis and algorithm development for the program

9 Data Analysis How many data items are needed? SOLUTION a character variable to hold the input data a counter to count the number of inputs Determine the input and output data items. INPUT: character data OUTPUT: count of characters

10 Algorithm Development INITIAL *Initialize *Read the character and count it *exit if it matches ‘q’ DETAILED *Make count=0 *Read the character input and add 1 to count until character input is equal to ‘q’ * Display count value and exit

11 Algorithm Development FINAL –Initialize the count to zero –Read a character and increment count –While (character is not equal to ‘q’) – (Read a character and increment count) –Display the count and exit

12 Programming Data analysis gives us the declarations Algorithm gives us the statements Here while statement is most suitable because the character input is checked before exiting the program It is advisable to display messages on each action to track the program well

13 Lab Session III-B Limits and bounds (Demo NOT required) Increment Operator ASCII and UNICODE Experiment 3.5 Simple Information Encryption Exercise 3-B (DEMO REQUIRED) Type Casting Experiment 3.6 (Demo NOT required)

Limits and Bounds The numerical data can be stored in the memory as a string of 1’s and 0’s There is an upper limit on the size of the numbers that can be represented in the computer The limits are recorded in the header file limits.h

Limits and Bounds Experiments 3.1(Step 1,2,3 ONLY) This experiment will show most negative integer Experiment 3.2 This experiment shows the result of exceeding the limits (Use unary decrement operator ‘i--’ in step 3)

Increment Operator In Experiment 3.2, we have seen the use of the unary increment operator ==> number++; i++ Similarly we have a unary decrement operator ==> number--, i-- Instead of number=number-1;

ASCII and UNICODE The alphabets and digits are represented by a code that has integer values ASCII code was originally 7 bits (128 values) Values from 00 to 1F are reserved for special non-printable control characters

ASCII and UNICODE ASCII was not sufficient as more symbols were needed ASCII was revised to “Latin-1”, an 8-bit code that can have 256 symbols Latin-1 can cover some European languages Computers are being used all over the world A unified coding system was needed

19 ASCII and UNICODE A consortium developed a standard code called UNICODE. This code has 16 bits, thus 65,536 code points are possible World languages have 200,000 symbols so all cannot be accommodated Values from 0 to 255 map to Latin-1 or ASCII so changes are not felt in English

20 ASCII and UNICODE UNICODE allocates code points to languages in an “official” way Number of code points given is more than the letters in each language to accommodate different forms of each letter Adding new words in English e.g. applets does not require new code points but adding new words in Japanese requires new points

21 Uncover the ASCII code Experiment 3.5 Why do we include ? What is toascii? What is toupper? What is tolower? (HINT: Use these functions in your program to find out)

22 Simple Encryption Techniques Once you are able to process a text string, you can convert the characters to their ASCII values The ASCII values are numeric. You can modify these values so that no one can understand what is in the string Exercise 3-B Change a user supplied character to its ASCII value, add 8 to it and print the new character. (DEMO REQUIRED)

23 Type Casting Type Casting or Coercion means forcing the changing of the type of a variable’s value For example, adding integers and floating point numbers together and assigning it to a floating point number Experiment 3.6