/in/foo.cc: In function 'int main()':
/in/foo.cc:6:19: warning: comparison of constant '1000' with boolean expression is always true [-Wbool-compare]
    6 |         if (500<=a<1000){
      |             ~~~~~~^~~~~
/in/foo.cc:6:16: warning: comparisons like 'X<=Y<=Z' do not have their mathematical meaning [-Wparentheses]
    6 |         if (500<=a<1000){
      |             ~~~^~~
/in/foo.cc:10:19: warning: comparison of constant '1500' with boolean expression is always true [-Wbool-compare]
   10 |   else if (1000<=a<1500){
      |            ~~~~~~~^~~~~
/in/foo.cc:10:16: warning: comparisons like 'X<=Y<=Z' do not have their mathematical meaning [-Wparentheses]
   10 |   else if (1000<=a<1500){
      |            ~~~~^~~
/in/foo.cc:13:19: warning: comparison of constant '2000' with boolean expression is always true [-Wbool-compare]
   13 |   else if (1500<=a<2000){
      |            ~~~~~~~^~~~~
/in/foo.cc:13:16: warning: comparisons like 'X<=Y<=Z' do not have their mathematical meaning [-Wparentheses]
   13 |   else if (1500<=a<2000){
      |            ~~~~^~~