Chapter 3 Flow Control

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Chapter 3 Flow Control

• By C. Shing
• ITEC Dept
• Radford University

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Objectives

• Understand how to use assignment statement
• Understand how to use conditional statement
• Understand how to use loop statement

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Assignment Statement

• Identifier assignment_operator expression
• Represents
• identifier identifier assignment_operator
• (expression)
• After evaluating the right hand side of ,
• it stores result to the left hand side
  identifier
• (i.e. memory) and change to the data type of
  left
• hand side

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Assignment Statement assignment operator

• Assignment operator
• , ,-, , /,
• Example
• x 3
• Means xx3

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Assignment Statement (Cont.)

• Identifier expression
• Both sides of data type should match. If not,
  then
• the right hand side of type will be widened
• automatically to the left hand side data type.
• Otherwise, warning message will be given
• for narrowing data type.

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Assignment Statement (Cont.)

• Type conversion
• Automatic conversion rule
• Manual conversion use casting

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Assignment Statement (Cont.)

• Automatic conversion rule
• The widest data type in an expression determines
  the
• data type of the expression
• unsigned type is wider than the corresponding
  type
• the rest from widest double, float, long,
  int, short (or char)
• Finally, the expression data type will be widened
  to
• the data type of the identifier

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Assignment Statement (Cont.)

• Examples
• unsigned u
• long g
• int i
• unsigned long ul
• ul u-3g i // right hand side result type
• // long is converted to unsigned long
• // before stored in ul

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Assignment Statement (Cont.)

• Examples
• unsigned u
• float f
• int i
• double db
• db u/3-if // right hand side result type
• // float is converted to double before
• // stored to db

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Assignment Statement (Cont.)

• Casting
• Identifier (left hand side type) expression

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Assignment Statement (Cont.)

• Examples
• unsigned u
• long g
• int i
• unsigned long ul
• i (int) (u-3g 4) // right hand side result
  type
• // is long

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Conditional Statement - if

• if, if .. else, ?, switch
• if form
• if (condition)

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Conditional Statement if (Cont.)

• Note condition is evaluated using short-circuit
• If condition consists of condition1 and
  condition2
• connected by a logic operator
• Condition1 condition2
• if condition1 is false,
• then it will not evaluate condition2
• Condition1 condition2
• if condition1 is true,
• then it will not evaluate condition2

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Conditional Statement if (Cont.)

• Example
• int x
• if (x 5)
• printf(Always TRUE is printed!\n)

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Conditional Statement if else

• if else form
• if (condition)
• else

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Conditional Statement if else (Cont.)

• Example
• if (xlty)
• min x
• else
• min y

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Conditional Statement ?

• form identifier
• (condition)?true partfalse part

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Conditional Statement ? (Cont.)

• Example (Same example as previous one)
• min (xlty) ? x y

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Conditional Statement switch

• switch form values cannot be range as in Visual
  Basic
• switch (expression)
• case value1
• break // quit the current (switch) statement
• case value2
• case value3
• break // do this part when value2 or value3

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Conditional Statement switch (Cont.)

• switch form (Cont.)
• case
• break
• default // everything else

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Conditional Statement switch (Cont.)

• Example
• switch (character)
• case a
• case A a_count
• break
• default
• printf(c is not a letter!\n, character)

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Loop Statement

• while
• do while
• for
• Steps of writing a loop
• Identify the loop body repetition part
• Identify condition that can make the
• repetition of loop body either true of false
• Make sure the first time, condition is true

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Loop Statement - while

• while form repeat loop body when condition is
• true pre-condition
• while (condition part)
• Note condition part can be more than one
  statement,
• separated by a comma
• Example while (scanf("c", character),
  character !'\n')
• What task does the statement above perform?

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Loop Statement - while

• Condition can be
• Counter control (definite loop) use counter
• Example
• int count1
• // the following prints out 5 times only
• while (count lt 5)
• count
• printf(d\n, count)

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Loop Statement - while

• Condition can be (Cont.)
• Sentinel control (indefinite loop)
• use pseudo data (sentinel) for condition
• Example sentinel data is any negative score
• int score
• scanf(d, score)
• while (score gt 0)
• printf(d\n, score)
• scanf(d, score)
• Yard-Meter Conversion

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Loop Statement - while

• Condition can be (Cont.)
• More than 1 statement
• Example
• Skip 1st Line

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Loop Statement while (Cont.)

• Example
• Hard to-find Error
• int x
• // the following is an infinite loop
• while (x 5)
• printf(Always TRUE is printed!\n)

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Loop Statement while (Cont.)

• Example (Use break to get out of loop)
• int x, count0
• // the following prints out TRUE 5 times
  only
• while (x 5)
• count
• printf(Always TRUE is printed!\n)
• if (count 5)
• break

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Loop Statement do while

• do while form repeat loop body when condition
• is true post-condition
• do
• while (condition)

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Loop Statement do while (Cont.)

• Example
• int x0
• do
• x
• printf(Always TRUE is printed!\n)
• while (x ! 5)

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Loop Statement - for

• for form repeat loop body when condition is
• true pre-condition
• Most general form can represent
• while and do while loops

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Loop Statement for (Cont.)

• for (initialization, exprPart1,
• exprPart2, ,condition
• exprPart3, ,last statement in loop body)

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Loop Statement for (Cont.)

• Example
• int i // loop index must be defined
• // outside for loop
• for (i0ilt5i)
• printf(TRUE is printed!\n) // print 5
  times

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Loop Statement for (Cont.)

• Example (Same as the previous one)
• int i0
• // print 5 times
• for (ilt5 printf(TRUE is printed!\n), i)

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Loop Statement for (Cont.)

• Example (Use continue statement to skip current
  loop)
• int x, count0
• // the following prints out TRUE 5 times
  only
• while (count lt10)
• count
• if (count 2 1) // skip odd number times
  of print
• continue
• printf(TRUE is printed!\n)

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Loop Statement for (Cont.)

• Represent while loop
• for (condition)

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Loop Statement for (Cont.)

• How to check end of file
• If read a character
• Use scanf(c, c)gt0 to read
• in a character to check any character being read
• (if reach to end of file, scanf returns -1)
• Example 1 a.out lt checkEOF.c
• If read an integer
• Use scanf(d, number)gt0 to read

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Loop Statement for (Cont.)

• Represent do while loop
• for (loop body statements, condition)

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Keyboard Input Format Function - scanf

• Form scanf(pure_format, variable_address)
• Format similar to those used in printf, however,
  no character or strings
• included
• i for decimal, octal (data begins with 0) or
  hexadecimal (data begins with 0x)
• If use s format, it reads all until it reaches
  the first white space
• variable represents the address of the memory
  (or variable)
• Example
• char c
• int i
• double db
• char s80 // remember s is address array of 80
  characters
• scanf(cdlfs, c, i, db, s)
• // sample dataa 100 -1.23 This is a sample data
• // ca, i100, db-1.23, sThis

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Class Example

• Example 1
• Example 2 print character 2
• in front of each line
• Read Character read a character after reading a
  
• number
• For loop

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Assignment

• Assignment 1

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Practice

• Given int a1,b2,c3,d4
• Find the values of the following table
• Expression Value
• ________ _____
• a bc a
• b cd5 b

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Practice - Answer

• Given int a1,b2,c3,d4
• Find the values of the following table
• Expression Value
• ________ _____
• a bc a 6
• b cd5 b 18

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References

• Herbert Schildt C The Complete Reference,
• 4th ed, Osborne Publishing
• Deitel Deitel C How to Program, 4th ed.,
• Chapter 3, 4 9, Prentice Hall