MPLAB X XC8 Error: 0: (499) undefined symbol (VS Code)

Question

I am new to coding in C and I cannot figure out the proper way to link my files together so that I can use code from one class in another. I'm working on a project which will likely become a very long program so I am trying to avoid cluttering my main class with a bunch of functions. Instead, I would like to keep them separate and make it easy to transfer the code into any future project.

From looking up similar issues I am assuming this is somewhat simple and that I am probably struggling so much with it because I'm missing the basics of coding in C.

This is what is shown in the terminal:

> Executing task in folder Led-Pot_Circuit_Test: .\Build.cmd 16f887 <


C:\Users\raymu_000\Documents\Programming\VisualStudioCode\PIC_C++_on_VSCode\Led-Pot_Circuit_Test>mkdir output-files
A subdirectory or file output-files already exists.

C:\Users\raymu_000\Documents\Programming\VisualStudioCode\PIC_C++_on_VSCode\Led-Pot_Circuit_Test>C:\Progra~1\Microchip\xc8\v2.32\bin\xc8.exe --chip=16f887 --outdir=".\output-files" ".\main.c"
C:\Progra~1\Microchip\xc8\v2.32\pic\bin\picc --chip=16f887 --outdir=.\output-files .\main.c
Microchip MPLAB XC8 C Compiler V2.32
Build date: Feb  1 2021
Part Support Version: 2.32
Copyright (C) 2021 Microchip Technology Inc.
License type: Node Configuration

0: (499) undefined symbol:
        _adc_convert(output-files\main.obj)
(908) exit status = 1
(908) exit status = 1

C:\Users\raymu_000\Documents\Programming\VisualStudioCode\PIC_C++_on_VSCode\Led-Pot_Circuit_Test>C:\Progra~1\Microchip\xc8\v2.32\bin\xc8.exe --chip=16f887 --outdir=".\output-files" ".\Project\InitApp.c"
C:\Progra~1\Microchip\xc8\v2.32\pic\bin\picc --chip=16f887 --outdir=.\output-files .\Project\InitApp.c
Microchip MPLAB XC8 C Compiler V2.32
Build date: Feb  1 2021
Part Support Version: 2.32
Copyright (C) 2021 Microchip Technology Inc.
License type: Node Configuration

Non line specific message: (1091) main function "_main" not defined
(908) exit status = 1
(908) exit status = 1
The terminal process "C:\WINDOWS\System32\WindowsPowerShell\v1.0\powershell.exe -Command .\Build.cmd 16f887" terminated with exit code: 1.

Terminal will be reused by tasks, press any key to close it.

My main class:

//main.c

// CONFIG1
#pragma config FOSC = INTRC_NOCLKOUT// Oscillator Selection bits (INTOSCIO oscillator: I/O function on RA6/OSC2/CLKOUT pin, I/O function on RA7/OSC1/CLKIN)
#pragma config WDTE = OFF       // Watchdog Timer Enable bit (WDT disabled and can be enabled by SWDTEN bit of the WDTCON register)
#pragma config PWRTE = OFF      // Power-up Timer Enable bit (PWRT disabled)
#pragma config MCLRE = OFF      // RE3/MCLR pin function select bit (RE3/MCLR pin function is digital input, MCLR internally tied to VDD)
#pragma config CP = OFF         // Code Protection bit (Program memory code protection is disabled)
#pragma config CPD = OFF        // Data Code Protection bit (Data memory code protection is disabled)
#pragma config BOREN = OFF      // Brown Out Reset Selection bits (BOR disabled)
#pragma config IESO = OFF       // Internal External Switchover bit (Internal/External Switchover mode is disabled)
#pragma config FCMEN = OFF      // Fail-Safe Clock Monitor Enabled bit (Fail-Safe Clock Monitor is disabled)
#pragma config LVP = OFF        // Low Voltage Programming Enable bit (RB3 pin has digital I/O, HV on MCLR must be used for programming)

// CONFIG2
#pragma config BOR4V = BOR21V   // Brown-out Reset Selection bit (Brown-out Reset set to 2.1V)
#pragma config WRT = OFF        // Flash Program Memory Self Write Enable bits (Write protection off)

#define _XTAL_FREQ 8000000 // 8Mhz

// #pragma config statements should precede project file includes.
// Use project enums instead of #define for ON and OFF.

#include <xc.h>
#include <pic16f887.h>
#include "Project\user.h"


void main(void) {

    //InitApp();

    unsigned short adc_value; // variable to hold ADC conversion result in/* Configure the oscillator for the device

    ANSELbits.ANS0 = 0; // Disable analog on pin RA0
    TRISAbits.TRISA0 = 0; // Set pin RA0 as output

    while(1) {
        PORTAbits.RA0 = 0; // Set RA0 to LOW
        // calculate wait time
        adc_value = adc_convert(1); // perform A/D conversion using input from channel 1 (AN1)
        __delay_ms(500); // Right shift adc_value two spaces to convert to milliseconds
        PORTAbits.RA0 = 1; // Set RA0 to HIGH
        adc_value = adc_convert(1);
        __delay_ms(500);
    }
}

This is my attempt at making a library so that I can "easily" transfer some useful code later onto another project:

//user.h

#ifndef USER_H
#define USER_H

void init_adc(void);
unsigned short adc_convert(unsigned char);

#endif

Useful code:

//InitApp.c

#include <xc.h>
#include <pic16f887.h>
#include "user.h"

/*
 Initialize the Analog to Digital Converter
 */
void init_adc(void) {
    TRISAbits.TRISA1 = 0b1; // Set pin RA1 as Input
    //ANCON0bits.ANSEL1   =0b1;
    ADCON1bits.VCFG0 = 0; // set v+ reference to Vdd
    ADCON1bits.VCFG1 = 0; // set v- reference to Vss (Gnd)
    ADCON1bits.ADFM = 1; // right justify the output
    ADCON0bits.ADCS = 0b01; // use Fosc/8 for clock source
    ADCON0bits.ADON = 1; // turn on the ADC
}

/*
 Preform an analog to digital conversion. 
@param channel The ADC input channel to use. 
@return The value of the conversion.
*/
unsigned short adc_convert(unsigned char channel) {
    ADCON0bits.CHS = channel; // select the given channel
    ADCON0bits.GO = 1; // start the conversion
    while(ADCON0bits.GO_DONE); // wait for the conversion to finish
    return(ADRESH<<8)|ADRESL; // return the result
}

Pic for reference:

Here are the contents of the "output-files" Folder, when I run the "Build.cmd" task all the files from the compiler go here, but I am missing a few (like ".hex" file) since the program cannot compile properly.

Do I need to have a main class inside of InitApp.c class? How does one properly compile and link C files together??

I would appreciate amy help and advice, thanks.