INFSCI 0015 Data Structures Lecture 4: Simple Loops

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INFSCI 0015 - Data StructuresLecture 4 Simple
Loops

• Peter Brusilovsky
• http//www2.sis.pitt.edu/peterb/0015-011/

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Course Logistics

• We are at a turning point
• We have got through C basics
• Are you able to follow?
• How challenging was the quiz?
• We are writing first small but meaningful
  programs
• Can you understand what is going on?
• This is the last chance to catch up

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Once more about INFSCI 0015

• Programming data structures
• Double load? No, but still not 1/2 1/2!
• Is this course for me?
• Students have different experience
• Good in programming ? lazy course
• Some programming experience ? OK
• No programming experience ? work hard

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What does in mean - work hard?

• Get an extra book (KR2 is not enough)
• Attend lectures and browse it again
• Do your reading
• Explore all examples - run, modify...
• Solve all problems
• Ask questions in the forums
• Come and talk with us, use office hours
• Spread the load over time

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Some tough problems

• How to start?
• How to type the program?
• How to compile and run?
• How to submit
• Which files?
• How to use drop box?
• How to update the submission?
• Read the instructions, watch the forums!

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Expressions again

• Expression something that has a value
• Types of expressions we know
• Literal constants 33 or 3.14
• Variables count
• Simple - two operands and operator 3 5
• Complex (count - (44 - 12) / 7) num
• Some expressions has side effect
• x 0 / is an operator! /
• printf(Hello, World!\n)

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From expressions to statements

• Statement expression with a semicolon
• 33
• 35
• x 0
• x y 0 / x (y 0) /
• printf(Hello, World!\n)
• To make sense an expression in statement should
  have side effect

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Block and sequential execution

• Block ..
• A group of statements
• Statements are sequentially executed
• Syntactically equivalent to a statement
• Example
• a a 1
• b a 2

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Block and sequential execution

• Flowcharts are used to show the control flow
  inside the program
• Sequential execution inside a block means that
  the control (over the processor) flows downwards
  from statement to next statement

a a 1
b a 2
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While loop

• while (expression)
• loopstatement
• nextstatement
• If expression is not 0 (true) - dive into the
  loop
• If expression is 0 (false) - skip to
  nextstatement
• I.e, while expression is true, do the loop

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While loop

• while (expression)
• statement1
• ...
• statementK
• nextstatement
• If expression is not 0 - dive into the loop
• If expression is 0 - skip to nextstatement
• I.e, while expression is not 0, do the loop

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Flowchart of the while loop
Yes
Expression is equal to 0?
No
Statement1
StatementK
Nextstatement
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Example 4_1 - Counting to Zero

• / Lecture 4 Example 1 - counting to zero
• Course 0015
• Author Peter Brusilovsky /
• include ltstdio.hgt
• main()
• int counter 5 / setting the counter /
• printf("Start counting...\n")
• while (counter)
• printf("d\n" , counter)
• counter counter - 1
• printf("Fire!\n")

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Increment/decrement expressions

• Post-Increment num
• Side effect same as num num 1
• Value same as num
• Pre-Increment num
• Side effect same as num num 1
• Value same as num 1
• There are also pre and post-decrements
• count-- or --count

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Defining symbolic constants

• define is a preprocessor directive for defining
  symbolic constants
• Example
• define commission 3.0
• commission is a symbolic constant
• Now every appearance of commission is literally
  replaced by 3.0
• It is not a variable, it cant be assigned a value

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Example 4_2 - Counting to Zero

• / Lecture 4 Example 2 - counting to zero
• Author Peter Brusilovsky 9/12/00 /
• include ltstdio.hgt
• define HOW_MANY 5
• main()
• int counter HOW_MANY / setting the counter
  /
• printf("Start counting...\n")
• while (counter)
• printf("d\n" , counter--)
• printf("Fire!\n")

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Why to use symbolic constants?

• Remember example 2.1?
• / Temperature Converter /
• include ltstdio.hgt
• main()
• printf("100 Fahrenheit 6.2f Celsius\n",
  (5.0/9.0)(100-32))
• Need to replace 100 to 150 in two places (in real
  programs in dozens places!)

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Why to use symbolic constants?

• /
• New Example 2.1 Temperature Converter
• Author Peter Brusilovsky
• Objective use of define and printf
• /
• include ltstdio.hgt
• define FAHR 68.8 / the temperature to be
  converted /
• main()
• printf("6.2f Fahrenheit 6.2f Celsius\n",
• FAHR, (5.0/9.0)(FAHR-32))

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More About Preprocessor

• Preprocessor is a separate part of C compiler,
  which differs from the rest of it
• Makes file insertions
• include ltstdio.hgt
• Resolves definitions
• define NUM 100.0
• Removes comments
• / this is simply a comment /

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Example 2_1

• /
• Example 2.1 Temperature Converter
• Author Peter Brusilovsky
• Objective use of define and printf
• /
• include ltstdio.hgt
• define FAHR 100.0 / the temperature to be
  converted /
• main()
• printf("6.2f Fahrenheit 6.2f Celsius\n",
• FAHR, (5.0/9.0)(FAHR-32))

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Example 2.1 after preprocessing

• ...content of the file stdio.h...
• main()
• printf("6.2f Fahrenheit 6.2f Celsius\n",
• 100.0, (5.0/9.0)(100.0-32))

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Example 4_3 More Interest

• main()
• int years / years the capital stays in bank /
• float interest_rate / interest rate in
  percents /
• float capital / capital in dollars /
• float annual_interest / annual interest in
  dollars /
• printf("Startup capital (.cc) ")
• scanf("f",capital)
• printf("Interest rate in percents (xx.xx) ")
• scanf("f",interest_rate)
• printf("How many years? ")
• scanf("d", years)
• while (years)
• annual_interest capital interest_rate /
  100
• capital capital annual_interest
• --years
• printf("New capital 9.2f\n", capital)