Digit code breaker

char num[4]={'7','0','5','1'};

char guess[4] = {0};
void setup()
{
  Serial.begin(9600);

}

void loop()
{
  char result[4] = {'X','X','X','X'};
  int resu=0;

  Serial.println("enter 4 digit number with different values");
  for(int i=0;i<4;i++){
    while(Serial.available()==0);
    guess[i] = Serial.read();
    if(guess[i] == num[i]) result[i] = 'V';
    Serial.print(guess[i]);
  }
  Serial.println();
  for(int j=0;j<4;j++){
    if(result[j] !='V'){
      for(int k=0;k<4;k++){
        if(guess[k] == num[j]) result[k] = '*';
      }
    }
  }
  for(int n=0;n<4;n++){
    Serial.print(result[n]);
    if(result[n] == 'V') resu++;
  }
  Serial.println();
  if(resu == 4) Serial.println("Congratulations");
  else Serial.println("Try again");

}