Difference of Unary operators ( += , =+ , ++x , x++ )

问题

What is the difference between these unary operators in C# ? . Can you provide me with example?

Please provide the name of each. :)

+= vs =+

++x vs x++

回答1:

This has no doubt been answered before, but anyway...

They differ in how they change the value and how they return the result.

The first two += and =+ behave in the way that the first increments a variable, the other sets a variable. They are not related. Observe the following code:

// +=
x = 1;
printf( x += 1 ); // outputs 2, the same as x = x+1
printf( x );      // outputs 2

// =+
x = 1;
printf( x =+ 1 ); // outputs 1, the same as x = 1;
printf( x );      // outputs 1

The next two, ++x and x++, differ in the order their function. ++x will increment your variable by 1 and return the result. x++ will return the result and increment by 1.

// ++x
x = 1;
printf( ++x ); // outputs 2, the same as x = x+1
printf( x );   // outputs 2

// x++
x = 1;
printf( x++ ); // outputs 1
printf( x );   // outputs 2

They are mostly useful for for loops and while loops.

In terms of speed, ++x is considered a lot faster than x++ since x++ needs to create an internal temporary variable to store the value, increment the main variable, but return the temporary variable, basically more operations are used. I learned this a looong time ago, I don't know if it still applies

回答2:

Let's visualize the first ones, += and =+.

Because "+" is action, "=" is assignment, so

+= is to add BEFORE assignment

=+ is a bit confusing with "+", it could be "-", for example a=+7 or a=-7, anyway, it's a direct assignment.

Similarly,

++x is "increment then return"

x++ is "return then increase"

回答3:

++x vs x++ are unary operators. ++x means pre increment and x++ means post increment.

int temp;
temp = 1;
Console.WriteLine(++temp); // Outputs 2
temp = 1;
Console.WriteLine(temp++); // outputs 1
Console.WriteLine(temp); // outputs 2

Prefix increment means:

The result of the operation is the value of the operand after it has been incremented.

Postfix increment means:

The result of the operation is the value of the operand before it has been incremented.

Now the following: += means temp += 10; // same as temp = temp + 10;

This =+ isn't a valid operator. If one does this:

str = + str;  // will throw an error.
int a;
a = +2; // sort of meaningless . 2 and +2 means same.

More here: Is there such thing as a "=+" operator?

https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/operators/increment-operator

来源：https://stackoverflow.com/questions/28358241/difference-of-unary-operators-x-x

标签

unary-operator