Can someone explain the ++ operator?

Question

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C#: what is the difference between i++ and ++i?

I see this operator (++) very often. I know what it does ultimately, but it seems like there's some rules I don't understand. For example, it seems to matter if you put it before or after the variable you're using it on. Can someone explain this?

Answer 1

The statement

x++;

is exactly equivalent to

x = x + 1;

except that x is evaluated only once (which makes a difference if it is an expression involving property getters).

The difference between the following two:

DoSomething(x++);   // notice x first, then ++
DoSomething(++x);   // notice ++ first, then x

Is that in the first one, the method DoSomething will see the previous value of x before it was incremented. In the second one, it will see the new (incremented) value.

For more information, see C# Operators on MSDN.

It is possible to declare a custom ++ operator for your own classes, in which case the operator can do something different. If you want to define your own ++ operator, see Operator Overloading Tutorial on MSDN.

Answer 2

http://msdn.microsoft.com/en-us/library/36x43w8w(v=VS.80).aspx

The increment operator (++) increments its operand by 1. The increment operator can appear before or after its operand:

The first form is a prefix increment operation. The result of the operation is the value of the operand after it has been incremented.

The second form is a postfix increment operation. The result of the operation is the value of the operand before it has been incremented.

Answer 3

well if you put it like

variable++

It first uses the variable and the increments it (+1) On the otherhand if you

++variable

It first increments the variable and then uses it

Answer 4

If you put the ++ operator before the variable, it is incremented first. If you put the ++ operator after the variable, it is incremented after.

For example(C#):

int x = 0; Console.WriteLine("x is {0}", x++); // Prints x is 0

int y = 0; Console.WriteLine("y is {0}", ++y); // Prints y is 1

Answer 5

If you put the ++ operator before the variable, it is incremented first. If you put the ++ operator after the variable, it is incremented after.

For example(C#):

int x = 0;
Console.WriteLine("x is {0}", x++); // Prints x is 0

int y = 0;
Console.WriteLine("y is {0}", ++y); // Prints y is 1

Hope this cleared it up.

Answer 6

Another way to see it... here are two functions that do the same as prefix/postfix ++. This illustrates that prefix is, in theory, faster, because no temporary variable is needed to store the "previous" value:

// same as x ++;
int PostfixIncrement(ref int x)
{
    int y = x;
    x = x + 1;
    return y;
}

// same as ++ x;
int PrefixIncrement(ref int x)
{
    x = x + 1;
    return x;
}