/in/foo.cc: In function 'int merge(int, int)':
/in/foo.cc:17:2: warning: this 'if' clause does not guard... [-Wmisleading-indentation]
  if(!a) return b; if(!b) return a;//?????
  ^~
/in/foo.cc:17:19: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'if'
  if(!a) return b; if(!b) return a;//?????
                   ^~
/in/foo.cc: In function 'int main()':
/in/foo.cc:51:16: warning: format '%c' expects argument of type 'char*', but argument 2 has type 'int' [-Wformat=]
   scanf("%c",ch);
                ^
/in/foo.cc:51:8: warning: 'ch' may be used uninitialized in this function [-Wmaybe-uninitialized]
   scanf("%c",ch);
   ~~~~~^~~~~~~~~