3.6 - סטראקטים - פתרון

פתרון – Struct ו־Union

סעיף 1 – יצירת struct פשוט

#include <stdio.h>

struct Student {
    char* name;
    int age;
    float avg;
};

int main() {
    struct Student s1;
    s1.name = "Amit";
    s1.age = 21;
    s1.avg = 89.5;

    printf("Name: %s\n", s1.name);
    printf("Age: %d\n", s1.age);
    printf("Average: %.2f\n", s1.avg);

    return 0;
}

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סעיף 2 – העתקת struct

struct Student s2 = s1;

printf("Copied student:\n");
printf("Name: %s\n", s2.name);
printf("Age: %d\n", s2.age);
printf("Average: %.2f\n", s2.avg);

s1.age = 30;
printf("s1 age: %d\n", s1.age);
printf("s2 age: %d\n", s2.age); // stays 21, because the copy is by value

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סעיף 3 – struct בתוך struct

struct Date {
    int day;
    int month;
    int year;
};

struct Student {
    char* name;
    int age;
    float avg;
    struct Date birth_date;
};

int main() {
    struct Student s1;
    s1.name = "Amit";
    s1.age = 21;
    s1.avg = 89.5;
    s1.birth_date.day = 3;
    s1.birth_date.month = 7;
    s1.birth_date.year = 2002;

    printf("Birth date: %02d/%02d/%d\n",
           s1.birth_date.day,
           s1.birth_date.month,
           s1.birth_date.year);

    return 0;
}

---

סעיף 4 – שימוש ב־union

union Data {
    int i;
    float f;
    char* str;
};

int main() {
    union Data d;

    d.i = 1234;
    printf("int: %d\n", d.i);

    d.f = 4.5;
    printf("float: %f\n", d.f);

    printf("int again: %d\n", d.i); // will be garbage, because float overwrote the memory
    return 0;
}

ה־union חולק את אותו תא זיכרון בין כל המשתנים, לכן רק השדה האחרון שהוגדר יהיה תקף.

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סעיף 5 – sizeof ובדיקת גדלים

printf("Size of Student: %lu\n", sizeof(struct Student));
printf("Size of Data: %lu\n", sizeof(union Data));

• גודל struct הוא סכום כל השדות (כולל padding – מרווחים פנימיים שהמחשב מוסיף).

• גודל union הוא גודל השדה הכי גדול.

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סעיף בונוס – סדר משפיע על גודל struct

struct A {
    char c;
    int i;
};

struct B {
    int i;
    char c;
};

printf("Size of A: %lu\n", sizeof(struct A)); // usually 8
printf("Size of B: %lu\n", sizeof(struct B)); // usually also 8, but sometimes less depending on alignment

// reason: padding - to align the variables per the processor's requirement, empty bytes are added.