ECE206 Programming

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ECE206 - Programming

• Lecture 3 Operators and Data Type
• 08/30/07

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Recap

• Programming environment
• Good programming style
• ALU design

CPU
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Arithmetic operators

• , -, , /, (modulus), --,
• Increment and Decrement
• prefix form x and --x
• postfix form x and x--
• Precedence of arithmetic operators
• highest , --
• middle , /,
• lowest , -

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Examples for , -- operators
... x 10 y x cout ltlt y // whats
y? cout ltlt x // whats x? y y cout ltlt
y // whats y? y coutltlty //whats
y?
... x 10 y x cout ltlt y // whats
y? cout ltlt x // whats x? y y cout
ltlt y // whats y? y coutltlty //whats
y? ...

• When using the prefix form, C performs the
  increment or decrement prior to obtaining the
  operands value
• When using the postfix form, C will obtain the
  operands value before incrementing or
  decrementing it.

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Examples for /, operators
include ltiostreamgt using namespace std int
main() int x, y x 10 y
3 cout ltlt x / y cout ltlt \n cout
ltlt x y return 0

• ,-,,/ can be applied to any data type
• the modulus operation yields the remainder of
  an integer division, so it can NOT be used on
  type float or double.
• When / is applied to an integer or a character,
  any remainder will be truncated.

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Relational operators

• Compare values, mostly used in control structures
• gt greater than
• gt greater than or equal to
• lt less than
• lt less than or equal to
• equal to
• ! not equal to

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Logical operators

• Deal with multiple conditions, also common used
  in control structures
• AND
• OR
• ! NOT
• Short circuit evaluation
• expr1 expr2 expr3
• expr1 expr2 expr3
• How to improve performance?

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Assignments

• a expr
• the value of expr is computed and saved in
  variable a
• a a b ? a b
• the values of b and a are summed and the result
  is stored in a
• Similar for a - b a b a / b a b

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Conditional operator

• ?
• One of C most fascinating operator
• Require three parameters
• Condition is evaluated. If true, return exp1 If
  false, return exp2.
• Can be used to replace if-else statement

condition ? exp1 exp2
cout ltlt (guess magic ? Right
...Sorry, you're wrong.)
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Variable declaration

• Specify name and type int a float b1.0
• Reserve space in memory and optionally
  initialize.
• Use reasonably long and informative names. DO NOT
  USE SINGLE-CHARACTER NAMES for variables other
  than iterators. Its case sensitive for C
  program.
• Variable type int, short, long, float, double,
  char, boolean, pointers ()
• The size of a variable is measured by how many
  bits it takes
• Describe the variables purpose in a comment.
• Variables need to be declared before the first use

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Basic data types
Type Typical Bit Width Typical
Range char 8 -128 to 127 int
(32-bit) 32 -2,147,483,648 to 2,147,483,6
47 float 32 3.4E-38 to 3.4 E38 double 64
1.7E-308 to 1.7E308 bool 1 true or
false void N/A valueless
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Round-off errors

• Finite memory space to represent infinite digits
  of real numbers
• Apply equality operator to float/double data is
  dangerous

double x 3.35e17 double y x20 if (ygtx)
cout ltlt y is greater than x"
Whats the output?
double x, y .. if (x y) cout ltlt x
equals to y"
double x, y .. if ( fabs(x-y) lt 1e-10 )
cout ltlt x equals to y"
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Mixed Type Expression

• Data of different types in a single expression
  are converted to the same type
• Explicit type conversion cast

int m9, n5 float x, y x float(m)/n y
m/n cout ltlt x ltlt endl cout ltlt y ltlt endl
char ch int i float f double d result ch /
i f d (f i)
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Constants

• Constants refers to fixed values that cannot be
  altered by the program.
• Example constants
• define intCons 50
• define charCons c
• define USAGE Usage Hello\n
• Another way
• const int intCons50
• const char charConsc
• Backslash character constants
• \n (new line), \t (tab)

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Common errors
int x y 5 if (x y) cout ltlt x equals
to y\n if (3ltxlt7) cout ltlt x is between 3
and 7\n If (x gt y) cout ltlt x is greater
or equal than y\n cout ltlt x divided by y
equals to ltlt x/y ltlt \n
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What do you need to know

• Operators
• Arithmetic
• Relational
• Logical
• Precedence of operators
• Assignment operators
• Data type
• Variable vs. Constant declaration
• Basic data type and their size