C語言遞歸實現數字轉英文單詞：支票打印核心算法

C語言遞歸實現數字轉英文單詞：支票打印核心算法

《C和指針》習題：編寫 void written_amount(unsigned int amount, char *buffer)，將無符號整數轉為英文大寫單詞（如 16312 → "SIXTEEN THOUSAND THREE HUNDRED TWELVE"）。

遞歸分治策略

• 按**千分位**（三位一組）遞歸處理高位。
• 每組三位數轉換：百位 → 十位/個位（特殊處理 10~19）。
• 遞歸返回後追加千分位單位（THOUSAND, MILLION, BILLION）。

完整代碼

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

void written_amount(unsigned int amount, char *buffer);

int main() {
    unsigned int num; scanf("%u", &num);
    char b[100] = {0};
    written_amount(num, b);
    puts(b);
    return 0;
}

void written_amount(unsigned int amount, char *buffer) {
    static int count = 0;  // 千分位計數
    char *w1_9[] = {"ZERO","ONE","TWO","THREE","FOUR","FIVE","SIX","SEVEN","EIGHT","NINE"};
    char *w10_19[] = {"TEN","ELEVEN","TWELVE","THIRTEEN","FOURTEEN","FIFTEEN","SIXTEEN","SEVENTEEN","EIGHTEEN","NINETEEN"};
    char *wty[] = {"","","TWENTY","THIRTY","FORTY","FIFTY","SIXTY","SEVENTY","EIGHTY","NINETY"};
    char *wdiv[] = {"HUNDRED","THOUSAND","MILLION","BILLION"};

    unsigned int high = amount / 1000;
    if (high) { count++; written_amount(high, buffer); }  // 遞歸處理高位

    int val = amount % 1000;  // 當前三位
    if (val >= 100) {
        strcat(buffer, " "); strcat(buffer, w1_9[val/100]);
        strcat(buffer, " "); strcat(buffer, wdiv[0]);  // HUNDRED
        val %= 100;
    }
    if (val >= 20) {
        strcat(buffer, " "); strcat(buffer, wty[val/10]);
        val %= 10;
    }
    if (val >= 10) {
        strcat(buffer, " "); strcat(buffer, w10_19[val%10]);
    } else if (val > 0) {
        strcat(buffer, " "); strcat(buffer, w1_9[val]);
    }

    if (count > 0) {
        strcat(buffer, " "); strcat(buffer, wdiv[count--]);
        strcat(buffer, " ");
    }
}

測試用例

設計亮點

• static count 跨遞歸層級傳遞千分位層數，無需額外參數。
• 字符串拼接直接在 buffer 上操作，調用者負責分配足夠空間。
• 處理 10~19 特殊詞彙，符合英語讀法習慣。

此算法是金融系統、報表生成中數字轉文字的基石實現。