c# - Never seen before C++ for loop

Question

I was converting a C++ algorithm to C#. I came across this for loop:

for (u = b.size(), v = b.back(); u--; v = p[v]) 
b[u] = v;

It gives no error in C++, but it does in C# (cannot convert int to bool). I really can't figure out this for loop, where is the condition?

Can someone please explain?

PS. Just to check, to adapt a VECTOR to a LIST does b.back() correspond to b[b.Count-1] ?

Answer 1

The condition of the for loop is in the middle - between the two semicolons ;.

In C++ it is OK to put almost any expression as a condition: anything that evaluates to zero means false; non-zero means true.

In your case, the condition is u--: when you convert to C#, simply add != 0:

for (u = b.size(), v = b.back(); u-- != 0; v = p[v]) 
    b[u] = v; //                     ^^^^ HERE