FOR statement

1

• FOR statement
• a compact notation for a WHILE
• e.g. sumgrades 0
• for (i 1 i lt 25 i)
• cin gtgt grade
• sumgrades sumgrades grade
• syntax
• Initialization Test
  Update
• for ( InitStatement Expression1 Expression2
  )
• statement

2

• Sum the first 100 integers
• WHILE DO WHILE
• sum 0 sum 0
• i 1 i 1
• while (i lt 100) do
• sum sum i sum sum i
• i i
• while(i lt 100)
• FOR
• sum 0
• for (i 1 i lt 100 i)
• sum sum i

3

• Nested FOR statement
• processes in 2 dimensions
• for (lastnum 1 lastnum lt 7 lastnum)
• for (number 1 number lt lastnum number)
• cout ltlt number
• cout ltlt endl
• will print
• 1
• 12
• 123
• 1234
• 12345
• 123456

4
Problem Print out the integers 5, 10, 15100
each on a separate line

• for (i5 ilt100 ii5)
• cout ltlt i ltlt endl
• i5
• while (ilt100)
• cout ltlt i ltlt endl
• ii5

• for (i1 ilt20 i)
• cout ltlt 5i ltlt end

5

• DOCUMENTATION
• Each program should contain
• 1. Comment Section
• PROGRAM name of program
• AUTHOR your name and SSN
• SYSTEM compiler and operating system
• DATE date
• PURPOSE short description of problem
  which program solves
• 2. Header Part
• include (all header files)

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• DOCUMENTATION
• 3. Declaration Part
• Use realistic names for constants
• Use realistic names for variables (and explain
  their use)
• 4. Statement Part
• Include about 10 comments on subtasks to be
  performed
• Include blank lines for readability
• Use indentation ( 4 spaces)
• Include prompts for keyboard input
• Line up long cin and cout
• e.g. cout ltlt . . . . ltlt . . . . ltlt . . . .
• ltlt . . . . ltlt . . . . ltlt endl

7
Setting Padding

• Padding Output
• - Padding refers to the character used to fill
  in the unused space in an output field.
• - By default the pad character for justified
  output is the space (blank) character.
• - This can be changed by using the setfill()
  manipulator

int ID 413225 cout ltlt "0123456789" ltlt
endl cout ltlt setw(10) ltlt ID ltlt endl cout ltlt
setfill('0') //pad with zeroes cout ltlt
setw(10) ltlt ID ltlt endl cout ltlt setfill(' ')
//reset padding to spaces
This will produce the output
0123456789 413225 0000413225
8
Scope

• The region of program code where it is legal to
  reference (use) an identifier.
• Example
• if (alpha gt 3)
• int n
• cin gtgt n
• beta beta n

The scope of the identifier n is the body of the
if statement.
9
Categories of Scope

• Local scope
• The scope of an identifier declared inside a
  block extends from the point of declaration to
  the end of that block.
• Global scope
• The scope of an identifier declared outside of
  all blocks extends from the point of declaration
  to the end of the entire file.

10
Local Scope (Example)

• int x
• while (x lt 0)
• int y
• cin gtgt y
• x x y

The scope of y is local to the body of the while
loop. The scope of x is nonlocal to the body of
the while loop.
11
Global Scope (Example)

• double d
• int main ()
• int y 0
• cin gtgt d
• if (d lt 0)
• d y
• return 0

The identifier d has a global scope. It can be
referenced anywhere in the program below where it
is declared, including inside main and in the
body of the if statement.
What if a second variable named d was declared in
main?
12
Name Precedence

• When a block declares a local identifier with the
  same name as a global identifier, the local
  identifier takes precedence.
• Example

double d 1.2 int main() double d 3.5
cout ltlt d // 3.5 is printed
13
Scope Rules

• Global identifier
• Declaration to the end of the file.
• Local identifier
• Declaration to the end of the block.
• Does not include any nested block that contains a
  locally declared identifier with the same name.

14
Scope Examples

• int a
• char c
• int main ()
• int a
• while ()
• int b
• char c
• return 0

15
Variables

• Recall that variables in C are made up of four
  parts
• Name
• Type
• Memory location
• Value

16
Lifetime

• The period of time during program execution when
  an identifier has memory allocated to it.
• A local variable's lifetime
• Starts when entering the block
• Ends when the block is exited.
• A global variable's lifetime
• Duration of the entire program.

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Lifetime Example

• // c is neither in scope, nor
  has
• // memory allocated to it
• while ()
• // c is allocated memory
• char c // c is in scope and has memory
• // c's memory is deallocated
• // c is neither in scope, nor
  has
• // memory allocated to it

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Lifetime ! Scope

• int a
• char c
• int main ()
• int a
• while ()
• int b
• char c
• return 0

The lifetime of global identifiers a and
c extends for the duration of the entire
program. However, the global variable a is not
in scope in main. It is hidden by the
local variable a declared in main. Likewise in
the while loop, the global variable c has memory
allocated to it but is not in scope.