运行 ID: 137042

Main.cc: In function ‘int main()’:
Main.cc:44:14: error: expected initializer before ‘+=’ token
    double len+=sqrt(pow(a[i],2)-1)*2;
              ^~
Main.cc:45:7: error: ‘len’ was not declared in this scope
    if(len>=20){
       ^~~
Main.cc:45:7: note: suggested alternative: ‘lem’
    if(len>=20){
       ^~~
       lem
Main.cc:42:10: warning: unused variable ‘lem’ [-Wunused-variable]
   double lem=0;
          ^~~