Transcript Logical Operator

Operator
Assignation (=).
• The assignation operator serves to assign
a value to a variable.
a = 5;
• It is necessary to emphasize that the
assignation operation always takes place
from right to left and never at the inverse.
a = b;
Example
int a, b; // a:? b:?
a = 10; // a:10 b:?
b = 4; // a:10 b:4
a = b; // a:4 b:4
b = 7; // a:4 b:7
Compound assignation
operators
(+=, -=, *=, /=, %=, >>=, <<=, &=,
^=, |=)
Example
• value += increase; is equivalent to value =
value + increase;
• a -= 5; is equivalent to a = a - 5;
• a /= b; is equivalent to a = a / b;
• price *= units + 1; is equivalent to price = price
* (units + 1);
Increase and decrease.
• Another example of saving language when
writing code are the increase operator (++) and
the decrease operator (--). They increase or
reduce by 1 the value stored in a variable. They
are equivalent to +=1 and to -=1, respectively.
Thus:
a++;
a+=1;
a=a+1;
are all equivalent in its functionality: the three
increase by 1 the value of a.
Arithmetic operators
( +, -, *, /, % )
The five arithmetical operations supported
by the language are:
+addition
-subtraction
*multiplication
/division
%module
Relational Operator
( ==, !=, >, <, >=, <= )
Relational operators
•
•
•
•
•
•
==Equal
!=Different
>Greater than
<Less than
>=Greater or equal than
<=Less or equal than
Example
•
•
•
•
•
(7 == 5)would return false.
(5 > 4)would return true.
(3 != 2)would return true.
(6 >= 6)would return true.
(5 < 5)would return false.
Example 2
Suppose that a=2, b=3 and c=6:
• (a == 5)would return false.
• (a*b >= c)would return true since (2*3 >=
6) is it.
• (b+4 > a*c)would return false since (3+4 >
2*6) is it.
• ((b=2) == a)would return true.
Logical Operator
( !, &&, || ).
NOT Logic operators
!(5 == 5)returns false because the expression at
its right (5 == 5) would be true.
!(6 <= 4)returns true because (6 <= 4) would be
false.
!truereturns false.
!falsereturns true.
Logic operators && and ||
First
Operand
a
True
Second
Operand
b
True
result
a && b
result
a || b
True
True
True
False
False
True
False
True
False
True
False
False
False
False
Example
• ( (5 == 5) && (3 > 6) ) returns false ( true
&& false ).
• ( (5 == 5) || (3 > 6)) returns true ( true ||
false ).
Conditional operator ( ? )
• The conditional operator evaluates an
expression and returns a different value
according to the evaluated expression,
depending on whether it is true or false.
• Its format is:
condition ? result1 : result2
• if condition is true the expression will
return result1, if not it will return result2.
Example
• 7==5 ? 4 : 3 returns 3 since 7 is not equal
to 5.
• 7==5+2 ? 4 : 3 returns 4 since 7 is equal
to 5+2.
• 5>3 ? a : b returns a, since 5 is greater
than 3.
• a>b ? a : b returns the greater one, a or
b.
•
•
•
•
•
•
/* Program COMPARES.C */
int main() /* This file will illustrate logical compares
{
int x = 11, y = 11, z = 11;
char a = 40, b = 40, c = 40;
float r = 12.987, s = 12.987, t = 12.987;
•
*/
/* First group of compare statements
•
•
•
•
•
if (x == y) z = -13; /* This will set z = -13
if (x > z) a = 'A'; /* This will set a = 65
if (!(x > z)) a = 'B'; /* This will change nothing
if (b <= c) r = 0.0; /* This will set r = 0.0
if (r != s) t = c/2; /* This will set t = 20
•
*/
*/
*/
*/
*/
*/
/* Second group of compare statements */
•
•
•
•
•
if (x = (r != s)) z = 1000; /* This will set x = some positive
number and z = 1000
*/
if (x = y) z = 222; /* This sets x = y, and z = 222
*/
if (x != 0) z = 333; /* This sets z = 333
*/
if (x) z = 444;
/* This sets z = 444
*/
•
/* Third group of compare statements
•
•
•
•
•
•
•
•
*/
x = y = z = 77;
if ((x == y) && (x == 77)) z = 33; /* This sets z = 33
*/
if ((x > y) || (z > 12)) z = 22; /* This sets z = 22
*/
if (x && y && z) z = 11;
/* This sets z = 11
*/
if ((x = 1) && (y = 2) && (z = 3)) r = 12.00; /* This sets
x = 1, y = 2, z = 3, r = 12.00
*/
if ((x == 2) && (y = 3) && (z = 4)) r = 14.56; /* This doesn't
change anything
*/
•
/* Fourth group of compares
•
•
•
*/
if (x == x); z = 27.345; /* z always gets changed
*/
if (x != x) z = 27.345; /* Nothing gets changed
*/
if (x = 0) z = 27.345; /* This sets x = 0, z is unchanged */
•
•
}
•
/* Result of execution
•
(No output from this program.)
•
*/
return 0;
// Filename: RELAT1ST.CPP
// Prints the results of several relational operations
#include <iostream.h>
void main()
{
int high = 45;
int low = 10;
int middle = 25;
int answer;
answer = high > low;
cout << "High > low is " << answer << endl;
answer = low > high;
cout << "Low > high is " << answer << endl;
answer = middle == middle;
cout << "Middle == middle is " << answer << endl;
answer = high >= middle;
cout << "High >= middle is " << answer << endl;
answer = middle <= low;
cout << "Middle <= low is " << answer << endl;
answer = 0 == 0;
cout << "Bonus relation: 0 == 0 is " << answer << endl;
return;
}
Output
High > low is 1
Low > high is 0
Middle == middle is 1
High >= middle is 1
Middle <= low is 0
Bonus relation: 0 == 0 is 1