2. Following is an example of input statement in C++: cin >> sclr >> vec[2*i-1] >> mat[f(i,j)][j+k] >> t[i/3][j][k]; Note that subscripts can be expressions, including functions. Based on this example, write a BNF definition of the syntax of (all possible) input statements in C++. Do not in expand your definition beyond components shown in the above example