cant figure out how to fix this compile error

Question

evrything worked for a bit and changed to much to get it working again. dont really understand the error.

[![C:\Users\bavob\AppData\Local\Temp\ccyfrkaL.ltrans0.ltrans.o: In function `loop':

C:\Users\bavob\Documents\Arduino\counte_up/counte_up.ino:96: undefined reference to `num_Write(int)'

collect2.exe: error: ld returned 1 exit status

exit status 1 Fout bij het compileren voor board Arduino/Genuino Uno]1]1

  { 1, 1, 1, 1, 1, 0, 1 }, // 0
  { 0, 1, 1, 0, 0, 0, 0 }, // 1
  { 1, 1, 0, 1, 1, 1, 0 }, // 2
  { 1, 1, 1, 1, 0, 1, 0 }, // 3
  { 0, 1, 1, 0, 0, 1, 1 }, // 4
  { 1, 0, 1, 1, 0, 1, 1 }, // 5
  { 1, 0, 1, 1, 1, 1, 1 }, // 6
  { 1, 1, 1, 0, 0, 0, 0 }, // 7
  { 1, 1, 1, 1, 1, 1, 1 }, // 8
  { 1, 1, 1, 0, 0, 1, 1 }  // 9
};

int pin = 2;
int buttonState = 0;
const int button = 12;
int led = 13;
int randVal;
bool pressVal;
void num_Write(int);
void setup() {
  pinMode(2, OUTPUT);
  pinMode(3, OUTPUT);
  pinMode(4, OUTPUT);
  pinMode(5, OUTPUT);
  pinMode(6, OUTPUT);
  pinMode(7, OUTPUT);
  pinMode(8, OUTPUT);
  pinMode(led, OUTPUT);
  Serial.begin(9600);
  pinMode(button, INPUT);
}

void loop() {
  buttonState = digitalRead(button);
  if (buttonState == LOW) {
    turnOff();
    pressVal = false;
  }
  else
  {
    if (pressVal == false)
    {
      randVal = rand() % 10;
      pressVal = true;
    }
    Serial.println(randVal);
    if (randVal == 0)
    {
      void zero(int number);
      num_Write(0);
    }
    else if (randVal == 1)
    {
      void one(int number);
      num_Write(1);
    }
    else if (randVal == 2)
    {
      void two(int number);
      num_Write(2);
    }
    else if (randVal == 3)
    {
      void three(int number);
      num_Write(3);
    }
    else if (randVal == 4)
    {
      void four(int number);
      num_Write(4);
    }
    else if (randVal == 5)
    {
      void five(int number);
      num_Write(5);
    }
    else if (randVal == 6)
    {
      void six(int number);
      num_Write(6);
    }
    else if (randVal == 7)
    {
      void seven(int number);
      num_Write(7);
    }
    else if (randVal == 8)
    {
      void eight(int number);
      num_Write(8);
    }
    else
    {
      void nine(int number);
      num_Write(9);
    }
  }
}

void zero(int number)
{
  for (int j = 0; j < 7; j++) {
    digitalWrite(pin, num_array[number][j]);
    pin++;
  }
}

void one(int number)
{
  for (int j = 0; j < 7; j++) {
    digitalWrite(pin, num_array[number][j]);
    pin++;
  }
}

void two(int number)
{
  for (int j = 0; j < 7; j++) {
    digitalWrite(pin, num_array[number][j]);
    pin++;
  }
}
void three(int number)
{
  for (int j = 0; j < 7; j++) {
    digitalWrite(pin, num_array[number][j]);
    pin++;
  }
}
void four(int number)
{
  for (int j = 0; j < 7; j++) {
    digitalWrite(pin, num_array[number][j]);
    pin++;
  }
}
void five(int number)
{
  for (int j = 0; j < 7; j++) {
    digitalWrite(pin, num_array[number][j]);
    pin++;
  }
}
void six(int number)
{
  for (int j = 0; j < 7; j++) {
    digitalWrite(pin, num_array[number][j]);
    pin++;
  }
}
void seven(int number)
{
  for (int j = 0; j < 7; j++) {
    digitalWrite(pin, num_array[number][j]);
    pin++;
  }
}
void eight(int number)
{
  for (int j = 0; j < 7; j++) {
    digitalWrite(pin, num_array[number][j]);
    pin++;
  }
}
void nine(int number)
{
  for (int j = 0; j < 7; j++) {
    digitalWrite(pin, num_array[number][j]);
    pin++;
  }
}
void turnOff()
{


}

Answer 1

You call function num_Write a lot, you create a forward declaration:

void num_Write(int);

But you forgot to create the implementation.

If you would have forgot the forward declaration the function would not be known at all (and you would get a compiler error). But with the forward declaration you let the compiler know the signature of num_write (so the return value and argument types).

When the linker wants to link all object (.o) files together it cannot find an implementation of the function num_write and you get this error. Hence ld is the linker.