Nested for loops

[chiquitina21]

I am totally lost with nested for loops. I have to write a C++ program that does the following:

1. Asks the user to enter an odd positive integer m.

2. Reads m from the user. If the value is not legal, the program repeatedly makes the user type in another value until a legal value of m has been entered.

3. Prints an m x m pattern in the shape of an asterisk. The pattern should appear as a large O printed from copies of the letter O that lies over a large - printed from copies of the character -.

so it should look something like this:
0_____-_____0
_0____-____0
___0___-___0
_____0__-__0
______0_-_0
____- - - 0 - - -
______0_-_0
_____0__-__0
____0___-___0
___0____-____0
__0_____-_____0

the underscores are just empty spaces so you get the idea.

how the heck am i suppose to do this?