Linker nie widzi funkcji z nagłówka

joł buły mam problem. rozdzieliłem program kalkulator RPN z książki K&R na różne pliki źródłowe + 1 nagłówek lecz podczas linkowania gcc wywala że main nie widzi deklaracji metod które są w nagłówku.
Kompiluję tak: gcc -Wall stack.c main.c getch.c getop.c -o RPNcalculator

A tu są poszczególne pliki:

calc.h:

#define NUMBER '0'

void Push(double);
double Pop(void);
int GetOp(char[]);
int GetCh(void);
void UnGetCh(int);

stack.c:

#include<stdio.h>
#include"calc.h"

#define stack_depth 100         //maximum stack depth

int stackpointer = 0;
double stack[stack_depth];

void push(double value)
{
        if(stackpointer < stack_depth)
                stack[stackpointer++] = value;
        else
                printf("stack full!\n");
}

double pop(void)
{
        if (stackpointer > 0)
                return stack[--stackpointer];
        else
        {
                printf("Stack empty!\n");
                return 0.0;
        }
}

main.c:

#include<stdio.h>
#include<stdlib.h>
#include"calc.h"

#define OP_MAX_SIZE 100 // maximum operand size

int main(void)
{
        int type;
        double operand2;
        char input[OP_MAX_SIZE];

                while((type = GetOp(input)) != EOF)
                {
                        switch(type)
                        {

                                /* OPERANDS */

                                case NUMBER:
                                        Push(atof(input));
                                        break;

                                /* OPERATORS */ 

                                case '+':
                                        Push(Pop() + Pop());
                                        break;
                                case '*':
                                        Push(Pop() * Pop());
                                        break;
                                case '-':
                                        operand2 = Pop();
                                        Push(Pop() - operand2);
                                        break;
                                case '/':
                                        operand2 = Pop();
                                        if (operand2 != 0.0)
                                                Push(Pop() / operand2);
                                        else
                                                printf("Cannot divide by zero!");
                                        break;

                                case '%':
                                        operand2 = Pop();
                                        if(operand2 != 0.0)
                                                Push((int) Pop() % (int) operand2);
                                        else
                                                printf("Cannot divide by zero!");
                                        break;

                                /* OTHER */

                                case '\n':
                                        printf("= %.8g\n", Pop());
                                        break;
                         }
                }

        return 0;
}

getch.c:

#include<stdio.h>

#define BUFFER_SIZE 100

char Buffer[BUFFER_SIZE];
int bfp = 0;            //buffer's next free position

int GetCh(void)
{
        return (bfp > 0) ? Buffer[--bfp] : getchar();
}

void UnGetCh(int character)
{
        if(bfp >= BUFFER_SIZE)
                printf("Too many characters!\n");
        else
                Buffer[bfp++] = character;
}

getop.c:

#include<stdio.h>
#include<ctype.h>
#include"calc.h"

int GetOp(char OpArray[])
{
        int i, next_character;

        //Skip all the blanks and tabs:
        while((OpArray[0] = next_character = GetCh()) == ' ' || next_character == '\t'); 

        OpArray[1] = '\0';
        if(!isdigit(next_character) && next_character != '.')
                return next_character; //if it's not a digit or deciman, return (not a number)
        i = 0;
        if(isdigit(next_character))
                while(isdigit(OpArray[++i] = next_character = GetCh()));

        if(next_character == '.')
                while(isdigit(OpArray[++i] = next_character = GetCh())); //Collect the fraction part

        OpArray[i] = '\0';
        if(next_character != EOF)
                UnGetCh(next_character);
        return NUMBER;
}

A to jest output od gcc:

/tmp/ccuaWFnU.o: In function `main':
main.c:(.text+0x47): undefined reference to `Push'
main.c:(.text+0x51): undefined reference to `Pop'
main.c:(.text+0x5e): undefined reference to `Pop'
main.c:(.text+0x6b): undefined reference to `Push'
main.c:(.text+0x75): undefined reference to `Pop'
main.c:(.text+0x82): undefined reference to `Pop'
main.c:(.text+0x8f): undefined reference to `Push'
main.c:(.text+0x99): undefined reference to `Pop'
main.c:(.text+0xa3): undefined reference to `Pop'
main.c:(.text+0xad): undefined reference to `Push'
main.c:(.text+0xb7): undefined reference to `Pop'
main.c:(.text+0xd7): undefined reference to `Pop'
main.c:(.text+0xe1): undefined reference to `Push'
main.c:(.text+0x102): undefined reference to `Pop'
main.c:(.text+0x122): undefined reference to `Pop'
main.c:(.text+0x141): undefined reference to `Push'
main.c:(.text+0x15c): undefined reference to `Pop'
collect2: ld returned 1 exit status

Z góry dzięki.

nvm napisałem pop i push z małej litery :/