Main.cc: In function 'int Prime_number(int)': Main.cc:5:26: error: 'sqrt' was not declared in this scope for(int i=2;i<=sqrt(n);i++){ ^ Main.cc: In function 'int main()': Main.cc:11:20: error: 'm' was not declared in this scope for(int i=6;i<=m;i+=2){ ^