Main.cc: In function ‘int main()’:
Main.cc:44:4: error: ‘len’ was not declared in this scope
len+=sqrt(pow(a[i],2)-1)*2;
^~~
Main.cc:44:4: note: suggested alternative: ‘lem’
len+=sqrt(pow(a[i],2)-1)*2;
^~~
lem
Main.cc:42:10: warning: unused variable ‘lem’ [-Wunused-variable]
double lem=0;
^~~