void sortera(char *filename, STUDENT *students, int numberOfStudents)
{
 STUDENT temp;
 int i,j;
 for(i=0; i<numberOfStudents; i++){
    for(j=0; j<i; j++){
        if(students[j].lastName<students[j+1].lastName){
            temp=students[j+1];
            students[j+1]=students[j];
            students[j]=temp;
        }
    }
 }
}