C言語のきほん「3教科の偏差値を表示してみよう」

/* 英語の点数と数学の点数と合計点の偏差値を求める*/

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

#define MAX_STUDENTS 100
#define SUBJECTS 3

typedef struct {
    char name[100];
    int scores[SUBJECTS]; // [0]:英語, [1]:数学, [2]:国語
    int total;
    double dev[SUBJECTS]; // 各教科の偏差値
    double total_dev;     // 合計点の偏差値
} Student;

/* 平均を計算 */
double mean(int data[], int n) {
    double sum = 0.0;
    for (int i = 0; i < n; i++)
        sum += data[i];
    return sum / n;
}

/* 標準偏差を計算 */
double stddev(int data[], int n, double avg) {
    double sum_sq = 0.0;
    for (int i = 0; i < n; i++)
        sum_sq += (data[i] - avg) * (data[i] - avg);
    return sqrt(sum_sq / n);
}

/* 偏差値を計算 */
double deviation(int score, double avg, double sd) {
    return 50 + 10 * (score - avg) / sd;
}

int main(void) {
    int n;
    Student students[MAX_STUDENTS];

    printf("生徒の人数を入力してください: ");
    scanf("%d", &n);

    // 点数入力
    for (int i = 0; i < n; i++) {
        printf("【%d人目】名前: ", i + 1);
        scanf("%s", students[i].name);
        printf("英語: "); scanf("%d", &students[i].scores[0]);
        printf("数学: "); scanf("%d", &students[i].scores[1]);
        printf("国語: "); scanf("%d", &students[i].scores[2]);
        students[i].total = students[i].scores[0] + students[i].scores[1] + students[i].scores[2];
    }

    // 各教科の平均・標準偏差を求める
    for (int subj = 0; subj < SUBJECTS; subj++) {
        int temp[MAX_STUDENTS];
        for (int i = 0; i < n; i++) {
            temp[i] = students[i].scores[subj];
        }

        double avg = mean(temp, n);
        double sd = stddev(temp, n, avg);

        for (int i = 0; i < n; i++) {
            students[i].dev[subj] = deviation(students[i].scores[subj], avg, sd);
        }
    }

    // 合計点の偏差値計算
    int totals[MAX_STUDENTS];
    for (int i = 0; i < n; i++) {
        totals[i] = students[i].total;
    }
    double avg_total = mean(totals, n);
    double sd_total = stddev(totals, n, avg_total);

    for (int i = 0; i < n; i++) {
        students[i].total_dev = deviation(students[i].total, avg_total, sd_total);
    }

    // 出力
    printf("\n【偏差値結果】\n");
    printf("No.\t名前\t英語\t数学\t国語\t合計偏差値\n");
    for (int i = 0; i < n; i++) {
        printf("%d\t%s\t%.2f\t%.2f\t%.2f\t%.2f\n",
               i + 1,
               students[i].name,
               students[i].dev[0],
               students[i].dev[1],
               students[i].dev[2],
               students[i].total_dev);
    }

    return 0;
}