[C言語][初心者]関数へのポインタとコールバック関数の違いと使い方

int func (int number)

int (*func_p) (int);

#include <stdio.h>

/*引数に１を足して返却する関数*/
int func_add(int number) {
    return number + 1; 
}
/*引数に１を引いて返却する関数*/
int func_sub(int number) {
    return number - 1;
}

int main() {
    int (*func_p) (int);
    
    //func_addをポインタ変数にセット、実行
    func_p = func_add;
    int numA = func_p(2);
    printf("func_add : %d\n", numA);

    //func_subをポインタ変数にセット、実行
    func_p = func_sub;
    int numB = func_p(2);
    printf("func_sub : %d\n", numB);
}

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

/*引数に１を足して返却するコールバック関数*/
int cb_add(int number) {
    return number + 1; 
}
/*引数に１を引いて返却するコールバック関数*/
int cb_sub(int number) {
    return number - 1;
}

//コールバック関数を呼び出す関数
void func_cb(int num, int (*cb)(int)) {
    printf("result:%d\n", cb(num));
}
int main() {
    int (*func_p) (int);
    char* s = "sub";
    
    func_p = NULL;
    if (strcmp("add", s) == 0) {
        func_p = cb_add;
        func_cb(5, func_p);
    }
    else if (strcmp("sub", s) == 0) {
        func_p = cb_sub;
        func_cb(5, func_p);
    }
    else {
        printf("unknown command\n");
    }
}

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

//
//typedef
//
//科目一覧
typedef enum {
    Jap = 3,
    Mat = 4,
    Eng = 5,
} Subject;

//生徒一覧
struct Student {
	int no;
	char* name;
	int total;
	int jap;
	int mat;
	int eng;
};

// グローバル変数
//科目
static Subject sub;
//点数
static int score;
//生徒
static struct Student student[] = {
    {	1, "yamada"	, 0, 0, 0, 0 },
    {	2, "fijita"	, 0, 0, 0, 0 },
    {	3, "tanaka"	, 0, 0, 0, 0 },
    {	4, "suzuki"	, 0, 0, 0, 0 },
};

//初期化メソッド
static void initScore_cb(struct Student* std) {
	std->jap = 0;
	std->mat = 0;
	std->eng = 0;
    std->total = 0;
    printf("No:%d name:%s init\n", std->no, std->name);
}

//セットメソッド
static void setScore_cb(struct Student* std) {
    switch(sub){
        case Jap:
            std->jap = score;
            break;
        case Mat:
            std->mat = score;
            break;
        case Eng:
            std->eng = score;
            break;
        default:
            return;
    }
    std->total = std->jap + std->mat + std->eng;
}

//結果メソッド
static void resultScore_cb(struct Student* std) {
    printf("-----------------------------------\n");
    printf("No:%d Name:%s TotalScore:%d\n", std->no, std->name, std->total);
}

//関数へのポインタ
typedef void (* command_func_t)(struct Student *std);

//コマンド一覧
static struct {
	char* cmd;
	command_func_t func;
	char *doc;
} command[] = {
	{ "score-init" 	, initScore_cb	,  "init set score test"    },
    { "score-set"	, setScore_cb	,  "set score"			    },
    { "score-result", resultScore_cb,  "result score"           },
	{ NULL          , NULL          , NULL                      }
};
// read command
static void readCommand(char* cmd, int no) {
	for (int i = 0; command[i].cmd; i++) {
		if (strcmp(command[i].cmd, cmd) == 0) {
            command[i].func(&student[no]);
			return;
		}
	}
}
// main
int main(int argc, char* argv[]) {
    //初期化
	readCommand("score-init", 0);
    readCommand("score-init", 1);
    readCommand("score-init", 2);
    readCommand("score-init", 3);

    //値をセット
    sub     = Jap;
    score   = 100; 
    readCommand("score-set", 3);
    sub     = Mat;
    score   = 88; 
    readCommand("score-set", 3);
    sub     = Eng;
    score   = 49; 
    readCommand("score-set", 3);
    sub     = Jap;
    score   = 27; 
    readCommand("score-set", 0);

    //結果
    readCommand("score-result", 0);
    readCommand("score-result", 1);
    readCommand("score-result", 2);
    readCommand("score-result", 3);
}