foo.cc: In function ‘bool check(int)’:
foo.cc:7:25: error: ‘mid’ was not declared in this scope
    7 |                 if(a[i]>mid){
      |                         ^~~
foo.cc:8:25: error: ‘b’ was not declared in this scope
    8 |                         b[cnt++]=a[i];
      |                         ^
foo.cc:12:20: error: ‘b’ was not declared in this scope
   12 |                 if(b[i]!=b[i+1]){
      |                    ^