Unit 3 · For Loops and Conditions

Last updated / 更新日期：2026-10-20

Course Home / 課程首頁 · Unit 1 / C++ 基礎

Start Here / 開始做題

1. Read the input and exact output format. 中文：先找輸入、輸出及換行要求。
2. Decide the start, stopping condition and update. 中文：先決定起點、停止條件及每次增減。
3. Trace a small input by hand. 中文：先用小數字手算每次迴圈。
4. Write, run and compare the sample; test the smallest input too. 中文：執行範例，也測試最小輸入。

Reading the Problem / 讀題須知

• Read what each input represents. N may be an upper limit, a number of values, a number of terms or a number of rows; use the meaning stated in that problem. 中文：先看 N 在該題代表甚麼，不要把「項數」與「數值上限」混為一談。
• [L, R] means every integer from L to R, including L and R. Read inputs in the listed order, even when the output counts down. 中文：區間包含兩端；倒序輸出不代表把輸入次序調轉。
• ... means the pattern continues; do not print the dots. N and sum in a mathematical expression stand for their actual values, not literal letters to print. 中文：省略號表示按規律繼續；輸出時用實際數字，不印省略號或變數名稱。
• N² means N multiplied by itself. In C++, use multiplication; ^ does not mean a square. 10^5 in a constraint means 100000, not C++ code to copy. 中文：題目中的平方及次方是數學記號，不可直接照抄成 C++ 運算。
• Output only the requested result. Do not add input prompts, labels or explanations. Use one space between adjacent numbers, no space at the start or end of a line, and a newline after the final output line, unless a problem states a different separator. 中文：只輸出指定結果；連加算式按題意使用加號，不能改為空格。
• Sample data demonstrates one case. Your program must also work for other valid inputs. 中文：範例只是其中一組資料，不可把範例的總和、次數或答案寫死。

Unit Dashboard / 單元地圖

C++ For Loop Syntax / for 迴圈格式

Use a for loop when the number of repetitions or the range is known. 中文：知道重複次數，或知道要走訪的數字範圍時，可使用 for。

Every C++ if, else if and else branch must also use { }, even for a single statement. 中文：C++ 的每個 if、else if 及 else 分支同樣必須使用大括號。

Every for loop in this course must use { }, even when the body contains only one statement. Put { after the closing ) and } after all repeated statements. 中文：本課程所有 for 迴圈必須使用 { }，即使只有一行指令也不可省略。) 後加入 {，所有重複執行的指令寫在大括號內，最後以 } 結束。

for (initialisation; condition; update) {
    // statements repeated each time
}

The syntax above is a template; replace the three parts with C++ expressions. 中文：上面是語法格式，不是直接執行的程式；三部分須換成實際 C++ 語句。

for (int i = 1; i <= 5; i++) {
    cout << i << '\n';
}

Execution order / 執行次序：initialise → check → body → update → check again.

Follow the arrows and predict what happens when i becomes 4. The diagram lists the printed values; the complete program below prints each on its own line. 中文：沿箭頭追蹤，先預測 i 變成 4 時走哪條路；圖中列出輸出數值，下方完整程式則把每個數字分行輸出。

Complete C++ Program / 完整程式

#include <iostream>
using namespace std;

int main() {
    int n;
    cin >> n;
    for (int i = 1; i <= n; i++) {
        cout << i << '\n';
    }
    return 0;
}

Input 3 prints 1, 2, 3 on three separate lines. 中文：輸入 3，便分三行輸出 1、2、3。

Dry Run / 完整手算追蹤

For n = 3:

Loop Variations / 常用寫法

Accumulators, Counters and Conditions / 累加、計數及條件

Keep sum and count outside the loop so they are not reset on each repetition. 中文：總和及計數器在迴圈外初始化；放在裡面會每次歸零。大數總和、階乘及平方使用 long long；平方可寫 1LL * i * i。

1LL is the integer 1 stored as long long. In 1LL * i * i, multiplication starts with that wider type. Storing the final result in long long alone does not prevent an earlier int multiplication from overflowing. 中文：1LL 令乘法從一開始就以 long long 計算；只把最後結果存入 long long，不能挽救乘法途中已發生的溢位。

Trace the same values 1, 2, 3, 4. Say which result would be wrong if its initial value were 0. 中文：用同一組數字比較兩種更新方式，再指出哪種運算不能以 0 作初值。

Conditions inside a Loop / 迴圈內的條件判斷

Check one score on each repetition. The condition decides whether the counter changes; both paths continue after the branch. 中文：每次迴圈檢查一個分數；只有符合條件才增加人數，兩條路最後都會繼續。

Output Separators / 空格與換行

For a sequence, print a space before every item except the first. For filtered values, use a bool first = true flag and change it after printing the first match. Print the final newline even when no value matches. 中文：第一個數字前不印空格；篩選數列可用 first 標記。沒有符合數字時，數列那一行仍須輸出換行。

bool stores true or false. Here, first means “no matching value has been printed yet”. 中文：first 起初為 true，表示還未印出第一個符合條件的數字。

If a task asks for a list, count and sum but no values match, the list line is blank and the count and sum are both 0. A blank line means printing a newline, not the words “blank line”. 中文：題目若要求「數列、數量、總和」，但沒有符合的數字，仍輸出三行：第一行留空，第二、三行各輸出 0；不要印出「空白行」三個字。

Nested For Loops / 巢狀迴圈

Point to where the inner loop restarts and where the newline is printed. 中文：指出每行內層迴圈的起點，以及換行應在甚麼時候發生。

for (int row = 1; row <= 3; row++) {
    for (int col = 1; col <= row; col++) {
        cout << '*';
    }
    cout << '\n';
}

The outer loop selects a row; the inner loop finishes that row. Put the row newline after the inner loop. 中文：外層決定行，內層完成該行；換行放在內層結束後。輸出為三行：*、**、***。

Common Errors / 常見錯誤

Supplement · Taxi Fare in C++ (if…else) / C++ 的士收費題目

Write a program in C++ to calculate and display the taxi fare using if...else. 中文：使用 C++ 的 if...else 編寫程式，輸入行駛里程（米），計算並輸出的士車資。

Sample Cases / 範例

Sample Input / 範例輸入

2600

Sample Output / 範例輸出

MOP 26

Reference Answer / C++ 參考答案

#include <iostream>
using namespace std;

int main() {
    long long distance;
    cin >> distance;
    long long fare;

    if (distance <= 1500) {
        fare = 20;
    } else {
        long long extra_distance = distance - 1500;
        long long blocks = (extra_distance + 499) / 500;
        fare = 20 + blocks * 2;
    }

    cout << "MOP " << fare << '\n';
    return 0;
}

How It Works / 計算說明

• cin >> distance;: read the distance in metres. 中文：輸入整數里程（米）。
• if (distance <= 1500) { ... }: use the base fare of 20. 中文：未超過 1500 米，收基本車資 20。
• else { ... }: calculate only the distance beyond 1500 metres. 中文：超過起步里程後，只計算超出的部分。
• (extra_distance + 499) / 500: both operands are integers, so / performs integer division. Adding 499 first counts an incomplete positive 500-metre block as a whole block. 中文：兩邊都是整數，/ 進行整數除法；先加 499，令不足 500 米的部分亦計作一段。
• cout << "MOP " << fare << '\n';: print MOP, one space and the fare. 中文：輸出貨幣單位、一個空格及車資，最後換行。

Boundary Checks / 邊界檢查

Examples / 例題

Each reference answer is a separate complete program. 中文：每個參考答案都是獨立完整程式，逐題複製執行。

Example 3-1 · Two Sequences

Sample Input / 範例輸入

(no standard input)

Sample Output / 範例輸出

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100
1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64 67 70 73 76 79 82 85 88 91 94 97 100

C++ focus / 語法重點：Use two separate for loops with { }; finish the first output line before starting the second / 兩個迴圈各輸出一行，數字之間只有一個空格。

Reference Answer / 參考答案

#include <iostream>
using namespace std;

int main() {
    for (int i = 1; i <= 100; i++) {
        if (i > 1) {
            cout << ' ';
        }
        cout << i;
    }
    cout << '\n';
    for (int i = 1; i <= 100; i += 3) {
        if (i > 1) {
            cout << ' ';
        }
        cout << i;
    }
    cout << '\n';
    return 0;
}

Example 3-2 · Sum from 1 to N

Sample Input / 範例輸入

10

Sample Output / 範例輸出

55

C++ focus / 語法重點：An accumulator keeps a running total. Initialise long long sum = 0; before the loop, then add each value / 累加器保存已有總和，在迴圈外初始化，避免每次歸零。

Reference Answer / 參考答案

#include <iostream>
using namespace std;

int main() {
    int n;
    cin >> n;
    long long sum = 0;
    for (int i = 1; i <= n; i++) {
        sum += i;
    }
    cout << sum << '\n';
    return 0;
}

Example 3-3 · Count Multiples

Sample Input / 範例輸入

1 20 3

Sample Output / 範例輸出

6

C++ focus / 語法重點：Use i % K == 0 to identify a multiple; increase the count by 1, not by i / 找到一個倍數就把數量加 1，不是加上該數值。

Reference Answer / 參考答案

#include <iostream>
using namespace std;

int main() {
    int l, r, k, count = 0;
    cin >> l >> r >> k;
    for (int i = l; i <= r; i++) {
        if (i % k == 0) {
            count++;
        }
    }
    cout << count << '\n';
    return 0;
}

Example 3-4 · Print 1 to N / 輸出 1 到 N

Sample Input / 範例輸入

5

Sample Output / 範例輸出

1 2 3 4 5

C++ focus / 語法重點：Initialise i at 1 and include N. Print a space only before the second and later values / 包含終點 N，第一個數字前不印空格。

Reference Answer / 參考答案

#include <iostream>
using namespace std;

int main() {
    int n;
    cin >> n;
    for (int i = 1; i <= n; i++) {
        if (i > 1) {
            cout << ' ';
        }
        cout << i;
    }
    cout << '\n';
    return 0;
}

Example 3-5 · Countdown / 倒數

Sample Input / 範例輸入

4

Sample Output / 範例輸出

4 3 2 1

C++ focus / 語法重點：Start at N and subtract 1 each time; the last printed value is 1 / 由 N 開始，每次減 1，最後印出 1。

Reference Answer / 參考答案

#include <iostream>
using namespace std;

int main() {
    int n;
    cin >> n;
    for (int i = n; i >= 1; i--) {
        if (i < n) {
            cout << ' ';
        }
        cout << i;
    }
    cout << '\n';
    return 0;
}

Example 3-6 · Sum of Even Numbers / 偶數總和

Sample Input / 範例輸入

10

Sample Output / 範例輸出

30

C++ focus / 語法重點：Start with the first positive even number and add 2 each time / 從第一個正偶數開始，每次加 2；N 是上限。

Reference Answer / 參考答案

#include <iostream>
using namespace std;

int main() {
    int n;
    cin >> n;
    long long sum = 0;
    for (int i = 2; i <= n; i += 2) {
        sum += i;
    }
    cout << sum << '\n';
    return 0;
}

Example 3-7 · Sum N Inputs / 加總 N 個輸入

Sample Input / 範例輸入

4
8 -2 5 1

Sample Output / 範例輸出

12

C++ focus / 語法重點：Read each value inside the loop and add it to the existing total / 迴圈內每次讀取一個數並累加，不能把所有輸入都放在迴圈之前。

Reference Answer / 參考答案

#include <iostream>
using namespace std;

int main() {
    int n;
    cin >> n;
    long long sum = 0;
    for (int i = 0; i < n; i++) {
        int x;
        cin >> x;
        sum += x;
    }
    cout << sum << '\n';
    return 0;
}

Example 3-8 · Count Passing Scores / 計算合格人數

Sample Input / 範例輸入

5
49 50 75 0 100

Sample Output / 範例輸出

3

C++ focus / 語法重點：Check each score inside the loop. Increase the counter only in the matching if branch, with { } / 每個分數都要判斷，只有合格時才把人數加一。

Reference Answer / 參考答案

#include <iostream>
using namespace std;

int main() {
    int n, count = 0;
    cin >> n;
    for (int i = 0; i < n; i++) {
        int score;
        cin >> score;
        if (score >= 50) {
            count++;
        }
    }
    cout << count << '\n';
    return 0;
}

Example 3-9 · Rectangle of Stars / 星號長方形

Sample Input / 範例輸入

2 4

Sample Output / 範例輸出

****
****

C++ focus / 語法重點：The outer loop selects a row; the inner loop prints all C stars. Put the newline after the inner loop / 外層處理行，內層印完該行星號後才換行。

Reference Answer / 參考答案

#include <iostream>
using namespace std;

int main() {
    int r, c;
    cin >> r >> c;
    for (int row = 1; row <= r; row++) {
        for (int col = 1; col <= c; col++) {
            cout << '*';
        }
        cout << '\n';
    }
    return 0;
}

Example 3-10 · Number Triangle / 數字三角形

Sample Input / 範例輸入

4

Sample Output / 範例輸出

1
1 2
1 2 3
1 2 3 4

C++ focus / 語法重點：The inner loop ends at the current row number, not always at N / 內層上限隨目前行號改變，不是每行都印 N 個數字。

Reference Answer / 參考答案

#include <iostream>
using namespace std;

int main() {
    int n;
    cin >> n;
    for (int row = 1; row <= n; row++) {
        for (int col = 1; col <= row; col++) {
            if (col > 1) {
                cout << ' ';
            }
            cout << col;
        }
        cout << '\n';
    }
    return 0;
}

Example 3-11 · Product from L to R / 區間連乘

Sample Input / 範例輸入

3 5

Sample Output / 範例輸出

60

C++ focus / 語法重點：Initialise product to 1 before the loop. Use the input bounds rather than fixed sample values. Every loop uses { }. 中文：乘積在迴圈外設為 1；起點及終點來自輸入，不可固定為範例的 3 和 5。

For L=3 and R=5: product changes from 1 → 3 → 12 → 60. If L=R, multiply that number once. 中文：若兩端相同，仍要執行一次；乘積初值若設為 0，結果會一直是 0。

Reference Answer / 參考答案

#include <iostream>
using namespace std;

int main() {
    int l, r;
    cin >> l >> r;
    long long product = 1;
    for (int i = l; i <= r; i++) {
        product *= i;
    }
    cout << product << '\n';
    return 0;
}

Example 3-12 · Addition Expression for Multiples / 倍數連加算式

Sample Input / 範例輸入

4 3

Sample Output / 範例輸出

3+6+9+12=30

C++ focus / 語法重點：For each i, the term is k * i. Start sum at 0, print + before every term except the first, and print = after the loop. 中文：第 i 項為 k × i；每次都累加該項，不是把總和固定設為範例的 30。

The picture uses N=3 and K=2; the sample above uses N=4 and K=3. Trace both with the same steps. 中文：圖解使用另一組 N=3、K=2；上方範例為 N=4、K=3，兩者使用同一套輸出步驟。

For N=4 and K=3, the terms are 3, 6, 9, 12 and sum changes 0 → 3 → 9 → 18 → 30. All statements between { and } repeat; the final = and total print once after }. 中文：大括號內的指令每次重複；等號及最後總和在迴圈結束後只輸出一次。

Reference Answer / 參考答案

#include <iostream>
using namespace std;

int main() {
    int n, k;
    cin >> n >> k;
    long long sum = 0;
    for (int i = 1; i <= n; i++) {
        int value = k * i;
        if (i > 1) {
            cout << '+';
        }
        cout << value;
        sum += value;
    }
    cout << '=' << sum << '\n';
    return 0;
}

ClassWork 3 / 課堂練習

Complete the assigned tasks independently. Submit source code and a screenshot of a successful run. 中文：獨立完成老師指定題目，提交原始碼及成功輸出截圖。

All exercises in this unit use ClassWork 3-x. Start with the basic loop tasks, then practise accumulation, conditions and nested loops. 中文：本章統一使用 ClassWork 3-x；先練習基本迴圈，再做累加、條件及巢狀迴圈。

ClassWork 3-1 · List Multiples of 7

Sample Input / 範例輸入

1 30

Sample Output / 範例輸出

7 14 21 28
4
70

Hint / 提示：Maintain both count and sum.

ClassWork 3-2 · Factorial

Sample Input / 範例輸入

5

Sample Output / 範例輸出

120

Hint / 提示：Start the product at 1.

ClassWork 3-3 · Multiples of Both A and B / 同時為 A、B 的倍數

Sample Input / 範例輸入

1 100 5 11

Sample Output / 範例輸出

55
1
55

Hint / 提示：Use logical AND: i % A == 0 && i % B == 0.

ClassWork 3-4 · Divisible by A or B

Sample Input / 範例輸入

1 30 13 29

Sample Output / 範例輸出

13 26 29
3
68

Hint / 提示：Use logical OR: ||.

ClassWork 3-5 · Alternating Squares

Sample Input / 範例輸入

2 7

Sample Output / 範例輸出

-27

Hint / 提示：Use parity of i - A to choose + or −.

ClassWork 3-6 · BMI

Sample Input / 範例輸入

60 1.75

Sample Output / 範例輸出

19.59

Hint / 提示：Use double, include <iomanip>, and use fixed with setprecision(2) / 以 double 計算，再固定輸出兩位小數。 Arithmetic and decimal-format revision; no loop is needed / 此題複習算術及小數格式，不需要迴圈。

ClassWork 3-7 · Addition Expression

Sample Input / 範例輸入

4

Sample Output / 範例輸出

1+2+3+4=10

Hint / 提示：Decide whether to print + before or after each number.

ClassWork 3-8 · Multiplication Table

Sample Input / 範例輸入

3

Sample Output / 範例輸出

1 2 3
2 4 6
3 6 9

Hint / 提示：Use nested for loops.

ClassWork 3-9 · Right Triangle

Sample Input / 範例輸入

4

Sample Output / 範例輸出

*
**
***
****

Hint / 提示：Outer loop controls rows; inner loop controls stars.

ClassWork 3-10 · Repeat a Message / 重複文字

Sample Input / 範例輸入

3

Sample Output / 範例輸出

Hello, F3!
Hello, F3!
Hello, F3!

Hint / 提示：Repeat N times / 執行 N 次。

ClassWork 3-11 · Ascending Range / 遞增區間

Sample Input / 範例輸入

-2 2

Sample Output / 範例輸出

-2 -1 0 1 2

Hint / 提示：Include both endpoints / 包含兩端。

ClassWork 3-12 · Descending Range / 遞減區間

Sample Input / 範例輸入

2 6

Sample Output / 範例輸出

6 5 4 3 2

Hint / 提示：Use i– / 每次減一。

ClassWork 3-13 · Odd Numbers / 奇數數列

Sample Input / 範例輸入

9

Sample Output / 範例輸出

1 3 5 7 9

Hint / 提示：Start at 1 and step by 2 / 從 1 開始，每次加 2。

ClassWork 3-14 · Sum of Squares / 平方總和

Sample Input / 範例輸入

4

Sample Output / 範例輸出

30

Hint / 提示：Use 1LL * i * i / 先以 long long 相乘。

ClassWork 3-15 · Count Positive, Negative and Zero / 正負及零計數

Sample Input / 範例輸入

6
-3 0 5 2 -1 0

Sample Output / 範例輸出

2 2 2

Hint / 提示：Use if / else if / else with three counters / 使用三個計數器。

ClassWork 3-16 · Passing Count and Score Sum / 合格人數與總分

Sample Input / 範例輸入

5
49 50 75 0 100

Sample Output / 範例輸出

3
225

Hint / 提示：Update both values only for a passing score / 合格才計數及累加。

ClassWork 3-17 · Largest Input / 最大值

Sample Input / 範例輸入

4
-8 -2 -5 -11

Sample Output / 範例輸出

-2

Hint / 提示：Use the first value as the initial maximum, then compare the remaining N−1 values. For -8, -2, -5, the maximum changes -8 → -2 → -2. If N=1, the only value is the maximum.
中文：全部數字都可能是負數，不能把最大值預設為 0；第一個數讀取後，不要再多讀 N 個數。

ClassWork 3-18 · Divisor List / 因數列表

Sample Input / 範例輸入

12

Sample Output / 範例輸出

1 2 3 4 6 12
6

Hint / 提示：Test N % i == 0 / 逐一檢查整除。

ClassWork 3-19 · Count Multiples of Exactly One / 只符合一個倍數條件

Sample Input / 範例輸入

1 12 2 3

Sample Output / 範例輸出

6

Hint / 提示：Use two bool conditions and compare them with != / 兩條件結果不同才計數。

ClassWork 3-20 · Inverted Star Triangle / 倒星號三角形

Sample Input / 範例輸入

4

Sample Output / 範例輸出

****
***
**
*

Hint / 提示：Decrease the inner bound each row / 每行減少內層次數。

ClassWork 3-21 · Sum of Odd Numbers / 奇數總和

Sample Input / 範例輸入

9

Sample Output / 範例輸出

25

Hint / 提示：Decide the first value and the step / 先決定第一個數及每次的步幅。

ClassWork 3-22 · Sum of Multiples of 3 / 三的倍數總和

Sample Input / 範例輸入

10

Sample Output / 範例輸出

18

Hint / 提示：Check whether the loop should run when N is 1 or 2 / 留意 N=1 或 2 時的結果。

ClassWork 3-23 · Total Spending / 支出總額

Sample Input / 範例輸入

5
12 8 15 0 5

Sample Output / 範例輸出

40

Hint / 提示：Read one amount on each repetition / 每次迴圈讀取一個金額。

ClassWork 3-24 · Sum of Input Squares / 輸入數值的平方總和

Sample Input / 範例輸入

4
-2 3 0 4

Sample Output / 範例輸出

29

Hint / 提示：Square the input value, not the loop counter / 平方的是讀入的數值，不是迴圈計數器。

ClassWork 3-25 · Count Excellent Scores / 計算高分人數

Sample Input / 範例輸入

6
79 80 100 60 85 0

Sample Output / 範例輸出

3

Hint / 提示：Increase the counter only when the score meets the condition / 符合條件時才增加計數。

ClassWork 3-26 · Rectangle of Hash Signs / 井號長方形

Sample Input / 範例輸入

2 4

Sample Output / 範例輸出

####
####

Hint / 提示：Finish one row before printing its newline / 完成一行的符號後才換行。

ClassWork 3-27 · Rectangle of One Number / 重複數字長方形

Sample Input / 範例輸入

2 3 7

Sample Output / 範例輸出

7 7 7
7 7 7

Hint / 提示：Distinguish the number to print from the row and column counters / 分清輸出數字與行、列計數器。

ClassWork 3-28 · Even Number Triangle / 偶數三角形

Sample Input / 範例輸入

4

Sample Output / 範例輸出

2
2 4
2 4 6
2 4 6 8

Hint / 提示：The number of values in a row depends on its row number / 每行的數字數量隨行號改變。

ClassWork 3-29 · Product of N Inputs / 輸入數值的乘積

Sample Input / 範例輸入

4
2 3 4 5

Sample Output / 範例輸出

120

Hint / 提示：Choose an initial product that does not make every result zero / 選擇不會令乘積一直為零的初值。

ClassWork 3-30 · Product of Even Values in a Range / 區間偶數連乘

Sample Input / 範例輸入

2 8

Sample Output / 範例輸出

384

Hint / 提示：Multiply only values that meet the even-number condition / 只把符合偶數條件的數字乘入。

ClassWork 3-31 · Odd Number Addition Expression / 奇數連加算式

Sample Input / 範例輸入

4

Sample Output / 範例輸出

1+3+5+7=16

Hint / 提示：Work out the odd value of each term before printing and adding it / 先求每一項的奇數，再輸出及累加。

ClassWork 3-32 · Even Number Addition Expression / 偶數連加算式

Sample Input / 範例輸入

4

Sample Output / 範例輸出

2+4+6+8=20

Hint / 提示：Print the equals sign and final sum after the repeated output / 重複輸出各項後，才輸出等號及最後總和。

Before Submission / 交功課前自查

• Did I use the required ClassWork 3-x number? 中文：題號是否正確？
• Does every for loop use { }, even for one statement? 中文：每個 for 是否都有大括號，沒有單行省略寫法？
• Does every C++ if, else if and else branch use { }? 中文：每個條件分支是否都有大括號？
• Is the loop start, condition and update correct? 中文：起點、條件及更新是否一致？
• Did I initialise sums to 0 and products to 1 outside the loop? 中文：累加、累乘初值是否正確？
• Does the output match spaces, lines and decimal places? 中文：空格、換行及小數位是否符合要求？
• Have I tested one repetition, both endpoints and no matching values where allowed? 中文：有否測試一次迴圈、邊界及無符合結果？

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