# Place a stone on an empty Go board

## C, 212195193181171132103 98 bytes

Saved 1 byte thanks to @FryAmTheEggman, 5 bytes thanks to @orlp

Call f() with the position to play (must be capitalized), and it prints out the resulting board.

i;f(char*p){for(i=380;i--;)putchar(i%20?i^20*atoi(p+1)+64-*p+(*p>72)?i%6^4|i/20%6^3?46:42:79:10);}


Try it on ideone.

### C (gcc), 132128 109

i;m;f(char*s){for(i=380;i--;putchar(m?m^84-*s+(*s>73)|(i/20+1)^atoi(s+1)?m%6^4|i/20%6^3?46:42:79:10))m=i%20;}


Ideone

A function that prints the board to STDOUT. Requires the letter coordinate to be capital. Printing in one loop seems to be slightly shorter than the previous nested loop approach.

## MATL, 33 bytes

'*O.'19: 6\4=&*Hj1&)Uw64-t8>-&(P)


Try it online!

### Explanation

'*O.'    % Push string with needed characters. Will be indexed into
19:      % Push numeric vector [1 2 ... 19]
6\4=     % 1 for values that equal 4 mod 6, 0 for the rest
&*       % Multiply by transposed version of itself with broadcast. This gives
% the 19×19 board with 0 instead of '.' and 1 instead of '*'
H        % Push 2. This will correspond to 'O' (stone)
j        % Input string, such as 'Q16'
1&)      % Split into its first char ('Q') and then the rest ('16')
U        % Convert to number (16)
w        % Swap, to move 'Q' to top
64-      % Subtract 64. Thus 'A' gives 1, 'B' gives 2 etc
t8>-     % Duplicate. Subtract 1 if it exceeds 8. This corrects for missing 'I'
&(       % Fill a 2 at coordinates given by the number and the letter
P        % Flip upside down, because matrix coordinates start up, not down
)        % Index the string '*O.' with the 19×19 array containing 0,1,2.
% Implicitly display