C# '++' Operator in conjunction with ToString()

Question

I needed to verify this in linqpad but this code evaluates to 0 the first time. Why does this occur in C#?

var integer = 0;
while(true){
    var @string = integer++.ToString();
    Console.WriteLine(@string);
}

I also verified that evaluates to 1 first.

var integer = 0;
while(true){
    var @string = (++integer).ToString();
    Console.WriteLine(@string);
}

I get the difference between ++x and x++. just was expecting it to do x++ and then the ToString() gets called.

Answer 1

My understanding of the post increment operator is that it first saves the value of the variable (i in this case), increments i and then uses the saved value (in this example, in the call to ToString()).

This code:

int i = 5;
string s = i++.ToString();

is equivalent to:

int i = 5;
int temp = i;
i = i + 1;
var s = temp.ToString();

You can use LinqPad or other tool (ILSpy, etc.) to look at the IL:

IL_0000:  nop         
IL_0001:  ldc.i4.5    
IL_0002:  stloc.0     // i
IL_0003:  ldloc.0     // i
IL_0004:  dup         
IL_0005:  ldc.i4.1    
IL_0006:  add         
IL_0007:  stloc.0     // i
IL_0008:  stloc.2     // CS$0$0000
IL_0009:  ldloca.s    02 // CS$0$0000
IL_000B:  call        System.Int32.ToString
IL_0010:  stloc.1     // s
IL_0011:  ret         

Here's a blog post by Eric Lippert with more information