Random number/sequence output
Even though this is not elegant by any means, for now this is what I've came out with:

typedef struct
{
  char naming[20];
} student;

student record[] {
  {""},
  {""},
};

int a = 0;

char buf[20];

// the setup routine runs once when you press reset:
void setup() {
  Serial.begin(9600);    // initialize serial communication at 9600 bits per second
  while (!Serial);              // wait for Serial Monitor to open
  Serial.println("Program Starts \n Insert 2 students name:");  // Title of sketch
}

void loop() {
  if (readline(Serial.read(), buf, 20) &gt; 0) {
    if (a == 0) {
      Serial.print("First student: ");
      strncpy(record[a].naming, buf, 20);
      Serial.println(record[a].naming);
      a = 1;
    }
    else if ( a == 1) {
      Serial.print("Second student: ");
      strncpy(record[a].naming, buf, 20);
      Serial.println(record[a].naming);
    }

  }
}

int readline(int readch, char *buffer, int len) {
  static int pos = 0;
  int rpos;

  if (readch &gt; 0) {
    switch (readch) {
      case '\r': // Ignore CR
        break;
      case '\n': // Return on new-line
        rpos = pos;
        pos = 0;  // Reset position index ready for next time
        return rpos;
      default:
        if (pos &lt; len - 1) {
          buffer[pos++] = readch;
          buffer[pos] = 0;
        }
    }
  }
  return 0;
}


Basically by using int a, the program decides the sequences of the name. Although it will not repeat the sequence after the 2nd input (ie 1st>2nd>1st>2nd), at least the sequence is not randomize anymore. 

Btw thanks for the tips @chrisl!