simple makefile faults

Hello Ubuntu support,

I am testing the make function on Ubuntu Jammy:
-------------
PRETTY_NAME="Ubuntu 22.04.4 LTS"
NAME="Ubuntu"
VERSION_ID="22.04"
VERSION="22.04.4 LTS (Jammy Jellyfish)"
VERSION_CODENAME=jammy
ID=ubuntu
ID_LIKE=debian
HOME_URL="https://www.ubuntu.com/"
SUPPORT_URL="https://help.ubuntu.com/"
BUG_REPORT_URL="https://bugs.launchpad.net/ubuntu/"
PRIVACY_POLICY_URL="https://www.ubuntu.com/legal/terms-and-policies/privacy-policy"
UBUNTU_CODENAME=jammy
------------------

I have created 3 files in the same directory:

A) hello.cpp
#include "func.h"

int main() {
    func(20);
    func(100);

    return 0;
}

B) func.cpp
#include "func.h"

void func(int i) {
    std::cout << "You passed: " << i << std::endl;
}

C) func.h
#include<iostream>

void func(int i);

I have created a makefile called hello:
-----
all: hello.exe

hello.exe: hello.o func.o
        @echo "Linking object files: hello.o and func.o"
        g++ -o hello.exe hello.o func.o
        @echo "Executable hello.exe has been created"

hello.o: hello.cpp func.h
        @echo "compiling hello.cpp"
        g++ -c hello.cpp
        @echo "hello.o has been created"

func.o: func.cpp func.h
        @echo "compiling func.cpp"
        g++ -c func.cpp
        @echo "func.o has been created"
-----

I use the makefile with 'make hello' I get this message
-----
g++ hello.cpp -o hello
/usr/bin/ld: /tmp/ccFKwfPP.o: in function `main':
hello.cpp:(.text+0xe): undefined reference to `func(int)'
/usr/bin/ld: hello.cpp:(.text+0x18): undefined reference to `func(int)'
collect2: error: ld returned 1 exit status
make: *** [<builtin>: hello] Error 1
-----

I have checked everything plus looked on the web for makefile tutorials. I can't understand why the makefile won't work.

Do you have any suggestions?

Best regards
Chris