add check for student in multiple grades

exercises/practice/grade-school/.meta/example.c

@@ -24,6 +24,19 @@ static int compare_student_grades_and_names(const void *s1, const void *s2)
       return compare_student_names(student1, student2);
 }
 
+static bool are_students_in_multiple_grades(roster_t students)
+{
+   for (size_t i = 0; i < students.count; ++i)
+      for (size_t j = 0; j < students.count; ++j)
+         if (i != j
+             && !strncmp(students.students[i].name, students.students[j].name,
+                         MAX_NAME_LENGTH)
+             && students.students[i].grade != students.students[j].grade)
+            return true;
+
+   return false;
+}
+
 bool add_student(char *name, uint8_t grade)
 {
    bool added = false;
@@ -49,6 +62,9 @@ roster_t get_grade(uint8_t grade)
 {
    roster_t grade_roster = { 0 };
 
+   if (are_students_in_multiple_grades(roster))
+      return grade_roster;
+
    for (size_t i = 0; i < roster.count && grade_roster.count < MAX_STUDENTS;
         ++i) {
       if (roster.students[i].grade == grade) {

exercises/practice/grade-school/test_grade_school.c

@@ -60,7 +60,7 @@ static void test_a_student_cant_be_in_two_different_grades(void)
           (student_t) {1, "Aimee"},
           (student_t) {2, "Aimee"}}
    };
-   uint8_t desired_grade = 5;
+   uint8_t desired_grade = 2;
 
    populate_roster(&input);