# 電機一乙 11128271 蔡嘉泓 U-11 5/16 Hackmd作業
## Function-Pointer
## 1. Use qsort to sort an array with different ways:

1. Sort from small to large

2. Sort from large to small

3. Odd numbers first, then even numbers; from small to large。

#include <stdio.h>
#include <stdlib.h>


int compareAscending(const void *a, const void *b) {
    int num1 = *(const int *)a;
    int num2 = *(const int *)b;
    return (num1 - num2);
}

int main() {
    int arr[] = {5, 2, 8, 1, 9};
    int size = sizeof(arr) / sizeof(arr[0]);
    qsort(arr, size, sizeof(int), compareAscending);
    printf("Sorted array in ascending order: ");
    for (int i = 0; i < size; i++) {
        printf("%d ", arr[i]);
    }
    return 0;
}


#include <stdio.h>
#include <stdlib.h>


int compareDescending(const void *a, const void *b) {
    int num1 = *(const int *)a;
    int num2 = *(const int *)b;
    return (num2 - num1);
}

int main() {
    int arr[] = {5, 2, 8, 1, 9};
    int size = sizeof(arr) / sizeof(arr[0]);
    qsort(arr, size, sizeof(int), compareDescending);
    printf("Sorted array in descending order: ");
    for (int i = 0; i < size; i++) {
        printf("%d ", arr[i]);
    }
    return 0;
}


#include <stdio.h>
#include <stdlib.h>


int compareOddEven(const void *a, const void *b) {
    int num1 = *(const int *)a;
    int num2 = *(const int *)b;
    if ((num1 % 2 == 0) && (num2 % 2 == 0)) {
        return (num1 - num2); 
    } else if ((num1 % 2 != 0) && (num2 % 2 != 0)) {
        return (num1 - num2); 
    } else if (num1 % 2 != 0) {
        return -1; 
    } else {
        return 1; 
    }
}
int main() {
    int arr[] = {5, 2, 8, 1, 9};
    int size = sizeof(arr) / sizeof(arr[0]);
    qsort(arr, size, sizeof(int), compareOddEven);
    printf("Sorted array with odd numbers first: ");
    for (int i = 0; i < size; i++) {
        printf("%d ", arr[i]);
    }
    return 0;
}


## 2. 優秀小組正在招募10個人員,根據以下要求,編寫一個處理程式。

1. 使用一個人員結構陣列,共有10個元素,每個元素為一個結構,包括以下欄位: 編號:整數(1...10)

是否已招募:0=未招募;1=已招募

。 姓名:80 個字元的陣列,存放招募人員姓名

該程式有以下選單: Choose a function, enter 0 to finish:

1) Show list of positions to be hired // Show numbers in a row

2) Show list of already hired positions (Sort by number)

3) Show list of already hired positions (Sort by name)

4) Hire a person // Input number and name to set a position

5) Fire a person // Input number to fire a person

本題請同學先完成選單的功能,當使用者選用某一項功能時,先印出功能之說明即可。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define MAX_NAME_LEN 80
#define NUM_POSITIONS 10

typedef struct {
    int number;
    int hired;
    char name[MAX_NAME_LEN];
} Position;

int cmp_by_number(const void *a, const void *b) {
    Position *pos_a = (Position *)a;
    Position *pos_b = (Position *)b;
    return pos_a->number - pos_b->number;
}

int cmp_by_name(const void *a, const void *b) {
    Position *pos_a = (Position *)a;
    Position *pos_b = (Position *)b;
    return strcmp(pos_a->name, pos_b->name);
}

void show_positions(Position positions[], int hired) {
    for (int i = 0; i < NUM_POSITIONS; i++) {
        if (positions[i].hired == hired) {
            printf("%d %s\n", positions[i].number, positions[i].name);
        }
    }
}

void hire_person(Position positions[]) {
    int number;
    char name[MAX_NAME_LEN];
    printf("Enter the number of the position to hire: ");
    scanf("%d", &number);
    getchar();
    printf("Enter the name of the person to hire: ");
    fgets(name, MAX_NAME_LEN, stdin);
    name[strcspn(name, "\n")] = 0;
    positions[number - 1].hired = 1;
    strcpy(positions[number - 1].name, name);
}

void fire_person(Position positions[]) {
    int number;
    printf("Enter the number of the position to fire: ");
    scanf("%d", &number);
    positions[number - 1].hired = 0;
}

int main() {
    Position positions[NUM_POSITIONS];
    for (int i = 0; i < NUM_POSITIONS; i++) {
        positions[i].number = i + 1;
        positions[i].hired = 0;
        strcpy(positions[i].name, "");
    }
    int choice;
    while (1) {
        printf("Choose a function, enter 0 to finish:\n");
        printf("1) Show list of positions to be hired\n");
        printf("2) Show list of already hired positions (Sort by number)\n");
        printf("3) Show list of already hired positions (Sort by name)\n");
        printf("4) Hire a person\n");
        printf("5) Fire a person\n");
        scanf("%d", &choice);
        if (choice == 0) {
            break;
        } else if (choice == 1) {
            show_positions(positions, 0);
        } else if (choice == 2) {
            qsort(positions, NUM_POSITIONS, sizeof(Position), cmp_by_number);
            show_positions(positions, 1);
        } else if (choice == 3) {
            qsort(positions, NUM_POSITIONS, sizeof(Position), cmp_by_name);
            show_positions(positions, 1);
        } else if (choice == 4) {
            hire_person(positions);
        } else if (choice == 5) {
            fire_person(positions);
        }
    }
    return 0;
}