/in/foo.cc: In function 'int main()':
/in/foo.cc:11:8: warning: statement has no effect [-Wunused-value]
    c[i]==b[i]-a[i];
    ~~~~^~~~~~~~~~~
/in/foo.cc:12:11: warning: statement has no effect [-Wunused-value]
      for(i-1;i<=M;i++)
          ~^~
/in/foo.cc:14:1: error: expected ';' before 'return'
 return 0;
 ^~~~~~