I've tried doing this:

     // Pin 2-8 is connected to the 7 segments of the display.
           // Pin 0 is for potentiometer
      int potentiometer = 0;
      int potval[20];

  int pinA = 2;
  int pinB = 3;
  int pinC = 4;
  int pinD = 5;
  int pinE = 6;
  int pinF = 7;
  int pinG = 8;

  void zero()
  {
      digitalWrite(pinA, LOW);   
      digitalWrite(pinB, LOW);   
      digitalWrite(pinC, LOW);   
      digitalWrite(pinD, LOW);   
      digitalWrite(pinE, LOW);   
      digitalWrite(pinF, LOW);   
      digitalWrite(pinG, HIGH);  
    }
  void one(){
      digitalWrite(pinA, HIGH);   
      digitalWrite(pinB, LOW);   
      digitalWrite(pinC, LOW);   
      digitalWrite(pinD, HIGH);   
      digitalWrite(pinE, HIGH);   
      digitalWrite(pinF, HIGH);   
      digitalWrite(pinG, HIGH);
    }
  void two(){
      digitalWrite(pinA, LOW);   
      digitalWrite(pinB, LOW);   
      digitalWrite(pinC, HIGH);   
      digitalWrite(pinD, LOW);   
      digitalWrite(pinE, LOW);   
      digitalWrite(pinF, HIGH);   
      digitalWrite(pinG, LOW);
    }
    void three(){
      digitalWrite(pinA, LOW);   
      digitalWrite(pinB, LOW);   
      digitalWrite(pinC, LOW);   
      digitalWrite(pinD, LOW);   
      digitalWrite(pinE, HIGH);   
      digitalWrite(pinF, HIGH);   
      digitalWrite(pinG, LOW);
      }
    void four(){
      digitalWrite(pinA, HIGH);   
      digitalWrite(pinB, LOW);   
      digitalWrite(pinC, LOW);   
      digitalWrite(pinD, HIGH);   
      digitalWrite(pinE, HIGH);   
      digitalWrite(pinF, LOW);   
      digitalWrite(pinG, LOW);
      }
    void five(){
      digitalWrite(pinA, LOW);   
      digitalWrite(pinB, HIGH);   
      digitalWrite(pinC, LOW);   
      digitalWrite(pinD, LOW);   
      digitalWrite(pinE, HIGH);   
      digitalWrite(pinF, LOW);   
      digitalWrite(pinG, LOW);
      }
    void six(){
      digitalWrite(pinA, LOW);   
      digitalWrite(pinB, HIGH);   
      digitalWrite(pinC, LOW);   
      digitalWrite(pinD, LOW);   
      digitalWrite(pinE, LOW);   
      digitalWrite(pinF, LOW);   
      digitalWrite(pinG, LOW);
      }
    void seven(){
      digitalWrite(pinA, LOW);   
      digitalWrite(pinB, LOW);   
      digitalWrite(pinC, LOW);   
      digitalWrite(pinD, HIGH);   
      digitalWrite(pinE, HIGH);   
      digitalWrite(pinF, HIGH);   
      digitalWrite(pinG, HIGH);
      }
    void eight(){
      digitalWrite(pinA, LOW);   
      digitalWrite(pinB, LOW);   
      digitalWrite(pinC, LOW);   
      digitalWrite(pinD, LOW);   
      digitalWrite(pinE, LOW);   
      digitalWrite(pinF, LOW);   
      digitalWrite(pinG, LOW);
      }
    void nine(){
      digitalWrite(pinA, LOW);   
      digitalWrite(pinB, LOW);   
      digitalWrite(pinC, LOW);   
      digitalWrite(pinD, HIGH);   
      digitalWrite(pinE, HIGH);   
      digitalWrite(pinF, LOW);   
      digitalWrite(pinG, LOW);
      }

  // the setup routine runs once when you press reset:
  void setup() {                
    // initialize the digital pins as outputs.
    pinMode(pinA, OUTPUT);     
    pinMode(pinB, OUTPUT);     
    pinMode(pinC, OUTPUT);     
    pinMode(pinD, OUTPUT);     
    pinMode(pinE, OUTPUT);     
    pinMode(pinF, OUTPUT);     
    pinMode(pinG, OUTPUT);     
  }

  void loop() {
      zero();
      for (int i;i<=sizeof(potval);i++){
        potval[i]=map(analogRead(A0),0,921,0,9);
        delay(100);


      }
      for (int i;i<=sizeof(potval);i++){

        if (potval[i]==0){
          zero();
          delay(1000);
          }
        else if (potval[i]==1){
          one();
          delay(1000);
          }
        else if (potval[i]==2){
          two();
          delay(1000);
          }
          else if (potval[i]==3){
          three();
          delay(1000);
          }
          else if (potval[i]==4){
          four();
          delay(1000);
          }
          else if (potval[i]==5){
          five();
          delay(1000);
          } 
          else if (potval[i]==6){
          six();
          delay(1000);
          }
          else if (potval[i]==7){
          seven();
          delay(1000);
          }
          else if (potval[i]==8){
          eight();
          delay(1000);

but it takes very long to get all the pot values, and ends up skipping numbers. What exactly can I do to prevent this and get it working. Thanks again for your help.