View Compilation Error

0_0_39765964_1384.cpp:13:3: error: storage size of 'a' isn't known
   13 |  }a[];
      |   ^
0_0_39765964_1384.cpp: In function 'int main()':
0_0_39765964_1384.cpp:31:39: error: expected primary-expression before ')' token
   31 |      while(scanf("%d %d",&m,&n)&&(m!=-)&&(n!=-))
      |                                       ^
0_0_39765964_1384.cpp:31:47: error: expected primary-expression before ')' token
   31 |      while(scanf("%d %d",&m,&n)&&(m!=-)&&(n!=-))
      |                                               ^
0_0_39765964_1384.cpp:35:14: error: expected primary-expression before ';' token
   35 |          sum=;
      |              ^
0_0_39765964_1384.cpp:37:16: error: expected primary-expression before ';' token
   37 |          for(i=; i < n; i++)
      |                ^
0_0_39765964_1384.cpp:47:16: error: expected primary-expression before ';' token
   47 |          for(i=;i<n;i++)
      |                ^