Chapter 02 (Part II)

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Chapter 02 (Part II)

• Introduction to C Programming

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Goal

• Example
• How to obtain information from the user.
• How to perform arithmetic calculations
• Introduction to computer memory.

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Obtaining Two Integers and Summing Them Up
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Variables

• We can store data in variables.
• Variable must be declared with name and data type
  before used.
• For example
• int integer1
• int integer2
• Several variables of same type can be written in
  one declaration. For example,
• int interger1, integer2, sum

Data type
Variable name
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Principles of naming a Variable

• The declaration of variables (in a block) cannot
  be duplicate.
• Use identifiers of 31 characters or fewer to
  ensure portability.
• Choosing meaningful identifiers.
• Avoid identifiers that begin with underscores.
• Always place a blank line between a declaration
  and adjacent executable statements.

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Capturing Input

• Input stream object
• stdcin
• Usually connected to keyboard
• Stream extraction operator gtgt
• Waits for user to input value until the user
  presses Enter.
• Stores value in variable to right of the operator
• Converts value to variable data type
• Example
• stdcin gtgt number1
• Reads an integer typed at the keyboard
• Stores the integer in variable number1

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Adding integers

• Assignment operator
• Assigns value on right to variable on left
• (correct) x 3
• (error) 3 x
• Binary operator (two operands)
• lvalue rvalue
• Example
• sum integer1 integer2
• Adding the values of integer1 and integer2
• Storing result in sum
• Remember the direction of assigning a value!
• int x 3
• int y x 2

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Outputting the Result

• Stream manipulator stdendl
• Outputs a newline.
• Flushes output buffer.
• Concatenating stream insertion operations
• Also called chaining or cascading.
• Stream insertion operator knows how to output
  each type of data.
• Example

sum number1 number2 stdcout ltlt "Sum is
stdcout ltlt sum stdcout ltlt stdendl
stdcout ltlt "Sum is " ltlt number1 number2 ltlt
stdendl
Outputs "Sum is Then, outputs sum of number1
and number2 Then, outputs newline and flushes
output buffer
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Obtaining Two Integers and Summing Them Up
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2.5 Memory Concept

• Variable names
• Correspond to actual locations (addresses) in
  computer's memory
• Every variable has name, type, size and value

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2.5 Memory Concept

• A compiler maintain a table that maps variable
  names to real addresses, and their types (memory
  size).

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2.5 Memory Concept

• Variable names
• When new value placed into variable, overwrites
  old value.
• Writing to memory is destructive.
• Reading variables from memory is nondestructive.
• Example
• sum number1 number2
• Value of sum is overwritten.
• Values of number1 and number2 remain intact.

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2.6 Arithmetic

• Arithmetic operators
• Modulus operator returns remainder
• 7 5 evaluates to 2
• Attempting to use the modulus operator () with
  non-integer operands is a compilation error.

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2.6 Arithmetic (Cont.)

• Straight-line form
• All constants, variables and operators appear in
  a straight line
• Grouping subexpressions
• Parentheses are used in C expressions to group
  subexpressions
• Example
• a ( b c )
• Multiple a times the quantity b c

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2.6 Arithmetic

• Rules of operator precedence
• Operators in parentheses evaluated first.
• Multiplication, division, modulus applied next
• Operators applied from left to right
• Addition, subtraction applied last
• Operators applied from left to right

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Exercise