undeclared variable problem

I am having a bit of problem understanding why the compiler is shouting at me that I have an undeclared variable.

This bit of code works:

Code:

void line(int n, char c)
{
  cout << callnumber << ": " ;

  for (int i = 0; i < n; i++)
    {
      cout << c ;
    }

  cout << endl ;
}

But this code gives me the following errors :

barchart.cc: In function `void hyphen(int)':
barchart.cc:7: `i' undeclared (first use this function)
barchart.cc:7: (Each undeclared identifier is reported only once
barchart.cc:7: for each function it appears in.)

Code:

void hyphen(int a)
{
  for (i = 0; i < a; i++)
    {
      cout << "-" ;
    }
  cout << endl ;
}

for (int i = 0; i < n; i++)
for (i = 0; i < a; i++)
Guess what this does...

Thank you.

As always, one is blind as a bat to the obvious.