foo.cc: In function 'void dfs(int, int, int, char)':
foo.cc:9:7: warning: suggest parentheses around assignment used as truth value [-Wparentheses]
   if(a=b&&ms>ans) ms=ans;
      ~^~~~~~~~~~
foo.cc:18:26: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
   if(a>b || a<b&&op!='+' &&a>0)
             ~~~~~~~~~~~~~^~~~~

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