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; ^~~