C# Conditional Operators
Description
C# has the following conditional operators:
| Operator | Meaning |
|---|---|
| & | AND |
| | | OR |
| ^ | XOR (exclusive OR) |
| || | Short-circuit OR |
| && | Short-circuit AND |
| ! | NOT |
True table,
| p | Q | p & q | p | q | p ^ q | !p |
|---|---|---|---|---|---|
| False | False | False | False | False | True |
| True | False | False | True | True | False |
| False | True | False | True | True | True |
| True | True | True | True | False | False |
AND operator
Boolean logical AND operator
class MainClass// w w w . ja v a 2 s .c o m
{
public static void Main()
{
bool result;
result = (1 == 1) && (2 > 1);
System.Console.WriteLine("(1 == 1) && (2 > 1) is " + result);
result = (1 == 1) && (2 < 1);
System.Console.WriteLine("(1 == 1) && (2 < 1) is " + result);
}
}
The code above generates the following result.
OR operator
Boolean logical OR operator
class MainClass/*w w w . j ava 2 s . co m*/
{
public static void Main()
{
bool result;
result = (1 == 1) || (1 == 0);
System.Console.WriteLine("(1 == 1) || (1 == 0) is " + result);
result = (1 == 0) || (1 == 0);
System.Console.WriteLine("(1 == 0) || (1 == 0) is " + result);
}
}
The code above generates the following result.
NOT operator
Boolean logical NOT operator
/* w w w . j av a 2s . co m*/
class MainClass
{
public static void Main()
{
bool result;
result = !(1 == 0);
System.Console.WriteLine("!(1 == 0) is " + result);
result = !(1 == 1);
System.Console.WriteLine("!(1 == 1) is " + result);
}
}
The code above generates the following result.
Logical operators with an if statement
Logical operators with an if statement
class MainClass// w w w .j a va2 s. c o m
{
public static void Main()
{
int intValue = 1500;
string stringValue = "closed";
if ((intValue > 1000) && (stringValue == "closed"))
{
System.Console.WriteLine("and");
}
}
}
The code above generates the following result.
Short-circuit evaluation
The && and || operators short-circuit evaluation when possible.
Shortcircuiting is essential in allowing expressions such as the following to run without throwing a NullReferenceException:
if (sb != null && sb.Length > 0){
}
Not short-circuit
The & and | operators test for and and or conditions as well:
The difference is that they do not short-circuit. For this reason, they are rarely used in place of conditional operators.
When to use Logic operator shortcut
shortcut means once the && or || knows the value of the whole bool expression, it stops the evaluation. For example, a && b is false if a is false regardless whether b is true or false. Under such condition C# doesn't execute b. shortcut is useful in the following expression:
if(i != 0 && 4/i == 2)
If i is 0 C# won't calculate 4/i, which throws DivideByZeroException.
using System;/* ww w . j av a2s . com*/
class Program
{
static void Main(string[] args)
{
int i = 0;
if (i != 0 && 4 / i == 2)
{
Console.WriteLine("here");
}
else {
Console.WriteLine("there");
}
}
}
The output:
The & and | don't do the shortcut.
&& vs &
//w w w . jav a2 s . com
using System;
class MainClass
{
static bool Method1()
{
Console.WriteLine("Method1 called");
return false;
}
static bool Method2()
{
Console.WriteLine("Method2 called");
return true;
}
static void Main()
{
Console.WriteLine("regular AND:");
Console.WriteLine("result is {0}", Method1() & Method2());
Console.WriteLine("short-circuit AND:");
Console.WriteLine("result is {0}", Method1() && Method2());
}
}
The code above generates the following result.
Side-effects of short-circuit operators
Side-effects of short-circuit operators
using System; /*w w w. ja v a 2 s. c o m*/
class Example {
public static void Main() {
int i;
bool someCondition = false;
i = 0;
Console.WriteLine("i is still incremented even though the if statement fails.");
if(someCondition & (++i < 100))
Console.WriteLine("this won't be displayed");
Console.WriteLine("if statement executed: " + i); // displays 1
Console.WriteLine("i is not incremented because the short-circuit operator skips the increment.");
if(someCondition && (++i < 100))
Console.WriteLine("this won't be displayed");
Console.WriteLine("if statement executed: " + i); // still 1 !!
}
}
The code above generates the following result.
