foo.cc: In function 'int main()':
foo.cc:18:50: warning: suggest parentheses around assignment used as truth value [-Wparentheses]
   18 |          else if (str[i]=='=') { c+=res*k; flag=k=1; res=0; }
      |                                                 ~^~
foo.cc:13:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   13 |     scanf("%s",str+1);
      |     ~~~~~^~~~~~~~~~~~

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