View Compilation Error

0_0_36657001_2862.cpp:12:11: error: size of array 'a' has non-integral type 'double'
 char a[5e4];
           ^
0_0_36657001_2862.cpp: In function 'int main()':
0_0_36657001_2862.cpp:68:19: error: request for member 'push_back' in 'a', which is of non-class type 'char [1]'
                 a.push_back (s[j][i % sz[j]]);
                   ^