Main.cc: In function 'int main()': Main.cc:8:12: error: redeclaration of 'double iq' double iq = iq / pow(2, b - 1); ^ Main.cc:6:12: note: 'double iq' previously declared here double iq = 100.0; ^ Main.cc:8:34: error: 'pow' was not declared in this scope double iq = iq / pow(2, b - 1); ^