foo.cc: In function 'int kinds(std::string, int)':
foo.cc:7:47: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
  if(sentence[start]>='3'||sentence[start]=='2'&&sentence[start+1]>'6')
                                               ^
foo.cc:7:4: warning: suggest explicit braces to avoid ambiguous 'else' [-Wparentheses]
  if(sentence[start]>='3'||sentence[start]=='2'&&sentence[start+1]>'6')
    ^
foo.cc:12:4: warning: suggest explicit braces to avoid ambiguous 'else' [-Wparentheses]
  if(sentence[start+1]=='0')
    ^