foo.cc: In function ‘int main()’:
foo.cc:16:12: warning: suggest explicit braces to avoid ambiguous ‘else’ [-Wdangling-else]
   16 |         if ((c[i]==')'||c[i]==']'||c[i]=='}')&&top)
      |            ^
foo.cc:32:19: warning: ‘mx’ may be used uninitialized [-Wmaybe-uninitialized]
   32 |     for (i=mx;i<mx+maxn;i++) printf("%c",c[i]);
      |                 ~~^~~~~
foo.cc:8:28: note: ‘mx’ was declared here
    8 |     int i,j,maxn=0,s=0,x=0,mx,l;
      |                            ^~