Problems in supporting programs that are out of my reach

Using Arduino Programming Questions
#1

This is a sketch I wrote to toggle the clock pin and the errors I received. I have a chinese UNO that pins 16 & 17 are labeled Scl & Sda and I was going to toggle them next.

Thanks for the help.

#define CLOCK_PIN 5
void loop()
{
pinMode (CLOCK_PIN, OUTPUT);
digitalWrite(CLOCK_PIN, LOW);
delay(50);
digitalWrite(CLOCK_PIN, HIGH);
delay(50);
}

C:\Users\user\AppData\Local\Temp\build2377632323531720214.tmp/core.a(main.cpp.o):
In function main': C:\Users\user\AppData\Roaming\Arduino15\packages\arduino\hardware\avr\1.6.2\cores\arduino/main.cpp:40: undefined reference to setup'
collect2.exe: error: ld returned 1 exit status
Error compiling.

#2

Where’s your setup() ?
And please post your code using the code tags, the </> in the message box, so that it looks like this:

Your code here.
#3

An Arduino program must have a function called setup() and a function called loop(). Either or both of them can be empty.

You should put your pinMode() statement in setup() as it only needs to be called once.

...R

#4

Try that:

#define CLOCK_PIN 5

void setup()
{
  pinMode (CLOCK_PIN, OUTPUT);
}


void loop()
{
  digitalWrite(CLOCK_PIN, LOW);
  delay(50);
  digitalWrite(CLOCK_PIN, HIGH);
  delay(50);
}
#5