const issues

Could someone assist me in modifying the below code to make the 2D array get set. It keeps telling me I need to use a const:
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	h = atoi(rows.c_str()); //put into int value
	w = atoi(cols.c_str()); //put into int value
	a = new char[h][w]; //set the size of the 2D array 

Thanks for any help
Also for a more biased/dissuading article: http://www.cplusplus.com/forum/articles/17108/
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