int histogram(char *filename, STUDENT *students, int numberOfStudents)
{
 int k,three=0,four=0,five=0,u=0;
 for(k=0; k<numberOfStudents; k++){
    if(students[k].grade=3)three++;
    if(students[k].grade=4)four++;
    if(students[k].grade=5)five++;
    if(students[k].grade=U)u++;
    }
 printf("%d%d%d%d, three, four, five, u");
}