Loop2:
for(int i=0; i<foo.Length; i++)
 Console.WriteLine(foo[i].ToString());

Loop3:
int len=foo.Length;
for(int i=0; i<len; i++)
 Console.WriteLine(foo[i].ToString());
In C/C++, we know that compared to Loop3, Loop2 does not need compute the length of foo again and again.
However,
different with C/C++
the performance of Loop3 is worse than Loop2.
C#code runs in a safe, managed enviroment. Every memory location is checked, including indexes.
For Loop3:
generated by complier:
int len=foo.length;
for(int i=0; i<len; i++)
{
 if(i<foo.Length)
  Console.WriteLine(foo[i].ToString());
 else
  throw new IndexOutOfRangeException();
}

ref: [Bill Wagner] Effective C#-50 Specific ways to improve Your C#.