Bonus Points

Finn and Jack helped to run the school's math competition, and the teacher rewards them: they each get 3 bonus points for every test. But no test can have more than 50 points, because that's the most a test could give.

This time, the function changes a student. If it got the student as Student student, it would change only its own copy, and the student in the array would stay the same. That's why it gets a pointer to the student: Student *student, the address of the student in the array. Through it, the function changes the original. You reach a structure's members through a pointer with an arrow, ->: student->points[i] means the same as (*student).points[i]. For example, a game where a player can have 5 lives at most:

#include <stdio.h>

typedef struct {
    char name[20];
    int lives;
} Player;

void add_lives(Player *player, int extra) {
    player->lives += extra;
    if (player->lives > 5) {
        player->lives = 5;
    }
}

int main(void) {
    Player players[] = {
        {"Tom", 2},
        {"Sara", 4},
    };
    add_lives(&players[0], 2);
    add_lives(&players[1], 2);
    printf("%s: %d lives\n", players[0].name, players[0].lives);
    printf("%s: %d lives\n", players[1].name, players[1].lives);
    return 0;
}

Tom: 4 lives
Sara: 5 lives

When you call the function, you give it the address of a student with &: &students[3] is the address of the student with index 3, Jack. Typical mistakes:

• Without the &, the compiler reports error: passing 'Student' to parameter of incompatible type 'Student *'; take the address with &. The end of the message even tells you what to do.
• With a dot instead of the arrow, student.points[i], it reports error: member reference type 'Student *' is a pointer; did you mean to use '->'?
• With const Student *student, the function isn't allowed to change the student, and the compiler reports error: cannot assign to variable 'student' with const-qualified type 'const Student *'.

The calls go in main(), above print_report(students, count);: first the points change, then they're printed. The other way round, the old points would be printed.