Adding RTC Library for Arduino Project in Visual Studio

Question

I am working in an Arduino project in visual studio. I need to get and set time to a RTC clock. That's why I am adding a ds3231 header file in my project from GitHub. When I want to build "it's showing me linking error.

cccSeqVu.ltrans0.o*: (.text.startup+0x1ea): undefined reference to DS3231_init(unsigned char)

My code is given below.

   #include <Wire.h>
   #include "ds3231.h"
void setup(){
    Wire.begin();
    DS3231_init(0x4);
}

void loop(){
}

Can anyone please help me to find out what I have missed.