drept.cpp:7: `float y1' redeclared as different kind of symbol /usr/include/bits/mathcalls.h:242: previous declaration of `double y1(double)' drept.cpp: In function `int main()': drept.cpp:26: `a' undeclared (first use this function) drept.cpp:26: (Each undeclared identifier is reported only once for each function it appears in.)