Sorting 3 arrays alphabetically

Greetings everyone,
I am writing a program that allows the user to enter the first name, last name, and grade of each student. The program then sorts all the names alphabetically by last name, and display a list of all the students names and grades in alphabetical order.
I don't understand how can I associate to print out the first name and the points o that same array.
I managed to make the output sort them by last name and output them, too. But the names remain unswapped.
So when I input:
Angelina Zellweger 11
Suzy Applegate 55
X Y 5

it should give:
Suzy Applegate 55
X Y 5
Angelina Zellwegerr 11

So far I managed to sort by last name and print them out. I just don't know how to associate the points and print them accordingly;

Code:

    int j;
      char tmp[20], tmp2[20];
      int posMin, tmp3;
      for (j=0; j<cnum-1; j++){
    posMin = j;

    for (i = j+1; i < cnum; i++)
      if (strcmp(cognome[i], cognome[posMin]) < 0)
	posMin = i;

    strcpy(tmp,cognome[j]);
    strcpy(cognome[j],cognome[posMin]);
    strcpy(cognome[posMin],tmp);

    strcpy(tmp2,nome[j]);
    strcpy(nome[j],nome[posMin]);
    strcpy(nome[posMin],tmp2);
      [b]
for (i = j+1; i<cnum; i++)
  {
    if(punteggio[i]>punteggio[posMin])
    {
    tmp3=punteggio[j];
    punteggio[j]=punteggio[posMin];
    punteggio[posMin]=tmp3;
      }
  }[/b]
      }	

The part in bold is wrong.
I am new to C so any help would be appreciated. Thank you