When does ++ not produce the same results as +1?

Question

The following two C# code snippets produce different results (assuming the variable level is used both before and after the recursive call). Why?

public DoStuff(int level) {   // ...   DoStuff(level++);   // ... } 

,

public DoStuff(int level) {   // ...   DoStuff(level+1);   // ... } 

After reading some of the responses below I thought it would be worthwhile posting the stack traces for level++, ++level and level+1 to highlight how deceiving this problem is.

I've simplified them for this post. The recursive call sequence starts with DoStuff(1).

// level++

DoStuff(int level = 1) DoStuff(int level = 2) DoStuff(int level = 2) DoStuff(int level = 2) 

// ++level

DoStuff(int level = 4) DoStuff(int level = 4) DoStuff(int level = 3) DoStuff(int level = 2) 

// level+1

DoStuff(int level = 4) DoStuff(int level = 3) DoStuff(int level = 2) DoStuff(int level = 1) 

Answer 1

To clarify all the other responses:

+++++++++++++++++++++

DoStuff(a++); 

Is equivalent to:

DoStuff(a); a = a + 1; 

+++++++++++++++++++++

DoStuff(++a); 

Is equivalent to:

a = a + 1; DoStuff(a); 

+++++++++++++++++++++

DoStuff(a + 1); 

Is equivalent to:

b = a + 1; DoStuff(b); 

+++++++++++++++++++++