hello-algo/zh-hant/codes/cpp/chapter_computational_complexity/iteration.cpp

/**
 * File: iteration.cpp
 * Created Time: 2023-08-24
 * Author: krahets (krahets@163.com)
 */

#include "../utils/common.hpp"

/* for 迴圈 */
int forLoop(int n) {
    int res = 0;
    // 迴圈求和 1, 2, ..., n-1, n
    for (int i = 1; i <= n; ++i) {
        res += i;
    }
    return res;
}

/* while 迴圈 */
int whileLoop(int n) {
    int res = 0;
    int i = 1; // 初始化條件變數
    // 迴圈求和 1, 2, ..., n-1, n
    while (i <= n) {
        res += i;
        i++; // 更新條件變數
    }
    return res;
}

/* while 迴圈（兩次更新） */
int whileLoopII(int n) {
    int res = 0;
    int i = 1; // 初始化條件變數
    // 迴圈求和 1, 4, 10, ...
    while (i <= n) {
        res += i;
        // 更新條件變數
        i++;
        i *= 2;
    }
    return res;
}

/* 雙層 for 迴圈 */
string nestedForLoop(int n) {
    ostringstream res;
    // 迴圈 i = 1, 2, ..., n-1, n
    for (int i = 1; i <= n; ++i) {
        // 迴圈 j = 1, 2, ..., n-1, n
        for (int j = 1; j <= n; ++j) {
            res << "(" << i << ", " << j << "), ";
        }
    }
    return res.str();
}

/* Driver Code */
int main() {
    int n = 5;
    int res;

    res = forLoop(n);
    cout << "\nfor 迴圈的求和結果 res = " << res << endl;

    res = whileLoop(n);
    cout << "\nwhile 迴圈的求和結果 res = " << res << endl;

    res = whileLoopII(n);
    cout << "\nwhile 迴圈（兩次更新）求和結果 res = " << res << endl;

    string resStr = nestedForLoop(n);
    cout << "\n雙層 for 迴圈的走訪結果 " << resStr << endl;

    return 0;
}