Need help making a flag that is design by user inputs, while using mainly array for it

[WildB]

Directions :
Write a program that will allow a user to create a flag of characters. The flag should be stored as a 2-dimensional array of characters. Your array should be of some maximum size but you should prompt the user to make alterations to it. Support the following options:

1. Allow the user to specify the square size in characters of the flag.
2. Allow the user to specify the default character.
3. Allow the user to enter stripes of a certain width, vertically and horizontally, and of a specific character.
4. Allow the user to enter a box filled with a certain character at specific locations on the flag.
5. Allow the user to enter diagonals across the flag of a certain character.
6. After each user specified change, you should output the new flag and prompt the user if they would like to make more changes or output the flag to a text file.

My code so far:

#include <iostream>
#include <string>

using namespace std;

int main()
{
int K,a ,b;
char ch, kh;
string mysize[100][100];
cout << "Enter a number for which you want the size of your flag to be: ";
cin >> K;
for (int i = 0; i < K; i++)
{
for (int j = 0; j < K; j++)
{
mysize[i][j];
}
}

cout << "Enter a character that will represent your flag: ";
cin >> ch;
for (int i = 0; i < K; i++)
{
for (int j = 0; j < K; j++)
{
mysize[i][j] = ch;

}
}
return 0;
}

Comments: I can do 1 and 2(Maybe 5 as well). Just need help with 3,4, and 6