# 適合國中生的 C 語言題目
## 題目 1：輸入名字，印出歡迎訊息
:::spoiler

#include <stdio.h>

int main() {
    char name[50];
    printf("請輸入你的名字：");
    scanf("%s", name);
    printf("Hello, %s！\n", name);
    return 0;
}

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## 題目 2：兩數加減乘除
:::spoiler

#include <stdio.h>

int main() {
    int a, b;
    printf("請輸入兩個整數：");
    scanf("%d %d", &a, &b);
    printf("加法: %d\n", a + b);
    printf("減法: %d\n", a - b);
    printf("乘法: %d\n", a * b);
    printf("除法: %d\n", b != 0 ? a / b : 0);
    return 0;
}

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## 題目 3：判斷奇數或偶數
:::spoiler

#include <stdio.h>

int main() {
    int n;
    printf("請輸入一個整數：");
    scanf("%d", &n);
    if (n % 2 == 0)
        printf("偶數\n");
    else
        printf("奇數\n");
    return 0;
}

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## 題目 4：九九乘法表
:::spoiler

#include <stdio.h>

int main() {
    int i, j;
    for (i = 1; i <= 9; i++) {
        for (j = 1; j <= 9; j++) {
            printf("%d×%d=%2d  ", i, j, i * j);
        }
        printf("\n");
    }
    return 0;
}

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## 題目 5：成績評分系統
:::spoiler
#include <stdio.h>

int main() {
int score;
printf("請輸入成績：");
scanf("%d", &score);

if (score >= 90)
printf("A 等級\n");
else if (score >= 80)
printf("B 等級\n");
else if (score >= 70)
printf("C 等級\n");
else
printf("需加強\n");

return 0;
}

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## 題目 6：三數找最大值
:::spoiler

#include <stdio.h>

int main() {
    int a, b, c, max;
    printf("請輸入三個整數：");
    scanf("%d %d %d", &a, &b, &c);

    max = a;
    if (b > max) max = b;
    if (c > max) max = c;

    printf("最大值是：%d\n", max);
    return 0;
}

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## 題目 7：數字總和（1+2+…+n）
:::spoiler

#include <stdio.h>

int main() {
    int n, sum = 0;
    printf("請輸入一個正整數：");
    scanf("%d", &n);

    for (int i = 1; i <= n; i++)
        sum += i;

    printf("總和是：%d\n", sum);
    return 0;
}

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## 題目 8：溫度轉換
:::spoiler

#include <stdio.h>

int main() {
    float celsius, fahrenheit;
    printf("請輸入攝氏溫度：");
    scanf("%f", &celsius);

    fahrenheit = celsius * 9 / 5 + 32;
    printf("華氏溫度是：%.2f\n", fahrenheit);
    return 0;
}

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## 題目 9：秒數轉時分秒
:::spoiler

#include <stdio.h>

int main() {
    int totalSeconds, hours, minutes, seconds;
    printf("請輸入總秒數：");
    scanf("%d", &totalSeconds);

    hours = totalSeconds / 3600;
    minutes = (totalSeconds % 3600) / 60;
    seconds = totalSeconds % 60;

    printf("%d 秒 = %d 時 %d 分 %d 秒\n", totalSeconds, hours, minutes, seconds);
    return 0;
}

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## 題目 10：簡易找零程式
:::spoiler

#include <stdio.h>

int main() {
    int cash;
    printf("請輸入金額：");
    scanf("%d", &cash);

    int a100 = cash / 100;
    cash %= 100;
    int a50 = cash / 50;
    cash %= 50;
    int a10 = cash / 10;
    cash %= 10;
    int a5 = cash / 5;
    int a1 = cash % 5;

    int sum = a100 + a50 + a10 + a5 + a1;
    printf("總共貨幣數量: %d\n", sum);
    printf("100元: %d\n", a100);
    printf("50元: %d\n", a50);
    printf("10元: %d\n", a10);
    printf("5元: %d\n", a5);
    printf("1元: %d\n", a1);
    return 0;
}

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## 題目 11：質數判斷
:::spoiler

#include <stdio.h>

int main() {
    int n, isPrime = 1;
    printf("請輸入一個整數：");
    scanf("%d", &n);

    if (n <= 1) isPrime = 0;
    for (int i = 2; i < n; i++) {
        if (n % i == 0) {
            isPrime = 0;
            break;
        }
    }

    if (isPrime)
        printf("%d 是質數\n", n);
    else
        printf("%d 不是質數\n", n);
    return 0;
}

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## 題目 12：費波那契數列（前 n 項）
:::spoiler

#include <stdio.h>

int main() {
    int n;
    printf("輸入你要幾個費波那契數：");
    scanf("%d", &n);

    int a = 0, b = 1;
    for (int i = 0; i < n; i++) {
        printf("%d ", a);
        int next = a + b;
        a = b;
        b = next;
    }
    printf("\n");
    return 0;
}

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## 題目 13：列出 1~n 的所有質數
:::spoiler

#include <stdio.h>

int main() {
    int n;
    printf("請輸入一個整數：");
    scanf("%d", &n);

    for (int num = 2; num <= n; num++) {
        int isPrime = 1;
        for (int i = 2; i * i <= num; i++) {
            if (num % i == 0) {
                isPrime = 0;
                break;
            }
        }
        if (isPrime)
            printf("%d ", num);
    }
    printf("\n");
    return 0;
}

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## 題目 14：成績平均與最大值
:::spoiler

#include <stdio.h>

int main() {
    int n, scores[100], sum = 0, max = 0;
    printf("請輸入成績數量：");
    scanf("%d", &n);

    for (int i = 0; i < n; i++) {
        printf("第 %d 筆成績：", i + 1);
        scanf("%d", &scores[i]);
        sum += scores[i];
        if (scores[i] > max) max = scores[i];
    }

    printf("平均：%.2f\n", (float)sum / n);
    printf("最高分：%d\n", max);
    return 0;
}

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## 題目 15：排序成績（氣泡排序）
:::spoiler

#include <stdio.h>

int main() {
    int n, scores[100];
    printf("請輸入成績數量：");
    scanf("%d", &n);

    for (int i = 0; i < n; i++) {
        scanf("%d", &scores[i]);
    }

    for (int i = 0; i < n - 1; i++) {
        for (int j = 0; j < n - i - 1; j++) {
            if (scores[j] > scores[j + 1]) {
                int temp = scores[j];
                scores[j] = scores[j + 1];
                scores[j + 1] = temp;
            }
        }
    }

    printf("排序後成績：");
    for (int i = 0; i < n; i++) {
        printf("%d ", scores[i]);
    }
    printf("\n");
    return 0;
}

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## 題目 16：統計票數
:::spoiler

#include <stdio.h>

int main() {
    int votes[4] = {0}, input, total;
    printf("請輸入總票數：");
    scanf("%d", &total);

    for (int i = 0; i < total; i++) {
        printf("請輸入票（1~3）：");
        scanf("%d", &input);
        if (input >= 1 && input <= 3)
            votes[input]++;
        else
            printf("無效票\n");
    }

    for (int i = 1; i <= 3; i++) {
        printf("候選人 %d 得票：%d\n", i, votes[i]);
    }
    return 0;
}

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## 題目 17：字串長度計算(模擬 strlen)
:::spoiler

#include <stdio.h>

int main() {
    char str[100];
    int len = 0;

    printf("請輸入字串：");
    scanf("%s", str);

    while (str[len] != '\0') {
        len++;
    }

    printf("字串長度為：%d\n", len);
    return 0;
}

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## 題目 18：簡易加密器（每字元 +1）
:::spoiler

#include <stdio.h>

int main() {
    char str[100];
    printf("請輸入英文（不含空格）：");
    scanf("%s", str);

    for (int i = 0; str[i] != '\0'; i++) {
        str[i]++;
    }

    printf("加密後：%s\n", str);
    return 0;
}

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## 題目 19：字串反轉
:::spoiler

#include <stdio.h>

int main() {
    char str[100];
    int len = 0;
    printf("請輸入字串：");
    scanf("%s", str);

    while (str[len] != '\0') len++;

    printf("反轉後：");
    for (int i = len - 1; i >= 0; i--) {
        printf("%c", str[i]);
    }
    printf("\n");
    return 0;
}

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## 題目 20：猜數字遊戲
:::spoiler

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

int main() {
    int answer, guess;
    srand(time(NULL));
    answer = rand() % 100 + 1;

    do {
        printf("猜一個 1 到 100 的數：");
        scanf("%d", &guess);
        if (guess > answer)
            printf("太大了！\n");
        else if (guess < answer)
            printf("太小了！\n");
    } while (guess != answer);

    printf("恭喜猜對了！\n");
    return 0;
}

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## 題目 21：井字遊戲（Tic-Tac-Toe）完整程式碼 - 雙人對戰版
:::spoiler

#include <stdio.h>

char board[3][3]; // 棋盤陣列

// 初始化棋盤
void initBoard() {
    for (int i = 0; i < 3; i++)
        for (int j = 0; j < 3; j++)
            board[i][j] = ' ';
}

// 顯示棋盤
void printBoard() {
    printf("\n");
    for (int i = 0; i < 3; i++) {
        printf(" %c | %c | %c \n", board[i][0], board[i][1], board[i][2]);
        if (i < 2)
            printf("---|---|---\n");
    }
    printf("\n");
}

// 檢查是否有玩家獲勝
char checkWinner() {
    // 橫列與直欄
    for (int i = 0; i < 3; i++) {
        if (board[i][0] != ' ' &&
            board[i][0] == board[i][1] && board[i][1] == board[i][2])
            return board[i][0];
        if (board[0][i] != ' ' &&
            board[0][i] == board[1][i] && board[1][i] == board[2][i])
            return board[0][i];
    }
    // 斜線
    if (board[0][0] != ' ' &&
        board[0][0] == board[1][1] && board[1][1] == board[2][2])
        return board[0][0];

    if (board[0][2] != ' ' &&
        board[0][2] == board[1][1] && board[1][1] == board[2][0])
        return board[0][2];

    return ' '; // 無人獲勝
}

// 檢查是否平手
int isDraw() {
    for (int i = 0; i < 3; i++)
        for (int j = 0; j < 3; j++)
            if (board[i][j] == ' ')
                return 0;
    return 1;
}

int main() {
    int row, col, player = 1;
    char symbol, winner = ' ';
    
    initBoard();

    printf("井字遊戲：玩家1 = X，玩家2 = O\n");

    while (1) {
        printBoard();
        symbol = (player == 1) ? 'X' : 'O';
        printf("玩家 %d (%c)，請輸入列與行（0~2）：", player, symbol);
        scanf("%d %d", &row, &col);

        // 檢查合法性
        if (row < 0 || row > 2 || col < 0 || col > 2 || board[row][col] != ' ') {
            printf("這個位置無效，請重新輸入！\n");
            continue;
        }

        board[row][col] = symbol;

        winner = checkWinner();
        if (winner != ' ') {
            printBoard();
            printf("玩家 %d (%c) 獲勝了！\n", player, winner);
            break;
        } else if (isDraw()) {
            printBoard();
            printf("遊戲平手！\n");
            break;
        }

        player = (player == 1) ? 2 : 1; // 換人
    }

    return 0;
}

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