exit status 1

i do not know what is the problem it this code.
I have been trying for days.... but its always the same.
I am new to this please help...

const int ml = 5;
const int mr = 6;
const int ml2 = 9;
const int mr2 = 10;
String voice;

void setup() {
pinMode(ml, OUTPUT);
pinMode(mr, OUTPUT);
pinMode(ml2, OUTPUT);
pinMode(mr2, OUTPUT);
Serial.begin (9600);
}

void loop() {
 {
  while (Serial.available()){ //Check if there is an available byte to read
     delay(10); //Delay added to make thing stable 
    char c = Serial.read(); //Conduct a serial read
    if (c == '#') {break;} //Exit the loop when the # is detected after the word
    voice += c; //Shorthand for voice = voice + c
  }
  if (voice.length() > 0){
    if(voice == "*go ahead")
    {
      forward(); //this is where the problem is.. 
      }
    if (voice == "*come back")
    {
      back();
    }
    if (voice == "*stop")
    {
      donontmove();
    }
  }
if (voice.length() > 0){
  if (voice == "*turn left")
  {
    left();
  }
  if (voice == "*turn right")
  {
    right
  }
  voice="";
}
void forward()
{
  digitalWrite(ml, HIGH);
  digitalWrite(mr, HIGH);
  digitalWrite(ml2, LOW);
  digitalWrite(mr2, LOW);
  return;
}
void left()
{
  digitalWrite(ml, LOW);
  digitalWrite(mr, HIGH);
  digitalWrite(ml2, HIGH);
  digitalWrite(mr2, LOW);
  return;
}
void right()
{
  digitalWrite(ml, HIGH);
  digitalWrite(mr, LOW);
  digitalWrite(ml2, LOW);
  digitalWrite(mr2, HIGH);
  return;
}
void donotmove()
{
  digitalWrite(ml2, LOW);
  digitalWrite(mr2, LOW);
  digitalWrite(ml, LOW);
  digitalWrite(mr, LOW);
}
void back()
{
   digitalWrite(ml2, HIGH);
  digitalWrite(mr2, HIGH);
  digitalWrite(ml, LOW);
  digitalWrite(mr, LOW);
}

it is always saying exit status 1
'forward' was not declared in this scope.

Wow is that code in a mess.

    if (voice == "*stop")
    {
      donontmove();
    }

This is trying to call a function that does not exist. Check the name

  if (voice == "*turn right")
  {
    right
  }

Which function are you calling here and how do you call a function ??

    void forward()
    {
      digitalWrite(ml, HIGH);
etc

Why is this function definition, and others, in the middle of the loop() function ?

Where is the end of the loop() function ? See previous question.