# 基礎程式設計參考程式碼

## 基礎程式設計
### Exercise 1

#include <iostream>
using namespace std;

int main() {
  cout << "Hello world!";
  return 0
}

### Exercise 1 without namespace

#include <iostream>

int main() {
  std::cout << "Hello world!";
  return 0;
}

### Example - 換行

#include <iostream>
using namespace std;

int main() {
  cout << "Hello world!\n";
  cout << "I am learning C++";
  return 0;
}

### Example - 註解 (1/2)

#include <iostream>

int main() {
  std::cout << "Hello world!"; // 列印出 Hello World
  return 0;
}

### Example - 註解 (2/2)

#include <iostream>
using namespace std;

int main() {
  /* The code below will print the sentence
  to the screen, and it is amazing */
  cout << "I want to become a maker!";
  return 0;
}

### Example - 先存入一個數值

#include <iostream>
using namespace std;

int main() {
  int myNum = 15; // 宣告myNum整數變數並把15存進去
  cout << myNum; // 列印出存入myNum中的數值
  return 0;
}

### Example - 先宣告再存入

#include <iostream>
using namespace std;

int main() {
  int myNum;
  myNum = 15;
  cout << myNum;
  return 0;
}

### Example - 指派新數值

#include <iostream>
using namespace std;

int main() {
  int myNum = 15;
  myNum = 10;
  cout << myNum;
  return 0;
}

### Exercise 2

#include <iostream>
using namespace std;

int main() {
  int myAge = 35
  cout << "I am " << myAge << "years old.";
  return 0;
}

### Example - cin 輸入

#include <iostream>
using namespace std;

int main() {
  int num;
  cout << "Type a number";
  cin >> num;
  cout << "Your number is: " << num;
  return 0;
}

### Example - 運算子

#include <iostream>
using namespace std;

int main() {
  int count = 1 + 2;  //右邊先做運算再存入左邊的變數
  cout << count;      //列印出數字
  return 0;
}

### Exercise 3

#include <iostream>
using namespace std;

int main() {
  int count = 3; // 宣告整數變數count為3
  count = count + 1; // 右邊先做運算再存入左邊變數，會取代原有的數值
  cout << count;
  return 0;
}

### Example - count 增加方式比較

#include <iostream>
using namespace std;

int main() {
  int count = 3;
  count += 1;
  cout << count;
  return 0;
}

#include <iostream>
using namespace std;

int main() {
  int count = 3;
  count ++;
  cout << count;
  return 0;
}

### Exercise 4

#include <iostream>
using namespace std;

int main() {
  int a = 5;
  int b = 2;
  cout << "The remainder is : " << a % b;
  return 0;
}

### Exercise 5

#include <iostream>
using namespace std;

int main() {
  int a = 1.02;
  float b = 1.02;
  cout << a << "\n" << b;
  return 0;
}

### Example - 運算精准度

#include <iostream>
using namespace std;

int main() {
  float num1 = 19.0;
  int num2 = 5;
  cout << num1 / num2;
  return 0;
}

#include <iostream>
using namespace std;

int main() {
  int num1 = 19;
  int num2 = 5;
  cout << num1 / num2;
  return 0;
}

### Exercise 6
**提示：**
1. 先宣告PI = 3.14159
2. 再宣告一個變數radius
3. 由使用者輸入radius的值
4. 做運算

<!-- :::spoiler **解答**

#include <iostream>
using namespace std;

int main() {
  double PI = 3.14159; // 宣告一個雙浮點數變數PI為3.14159
  double radius; // 宣告一個雙浮點數變數radius
  cout << "Please enter a radius: "; // 輸入一個數字後按enter
  cin >> radius; // 從鍵盤上抓取你所輸入的數字存入radius這個變數
  cout << "The area of this circle = ";
  cout << (PI*radius*radius); // 列印出運算出的結果
  return 0;
}

::: -->

### Example - 不好看的格式

#include <iostream>
using namespace std;

int main
    (
    ) {
  cout << "Learning C++ is fun";
            return 0;
}

### Example - 好看的格式

#include <iostream>
using namespace sd;

int main() {
  cout << "Learning C++ is fun";
  return 0;
}

### Example - 關係型

#include <iostream>
using namespace std;

int main() {
  int a = 3;
  int b = 5;
  int c;
  c = (a>b);
  cout << c <<"\n";
  c = (a<b);
  cout << c <<"\n";;
  return 0;
}

### Example - 邏輯型

#include <iostream>
using namespace std;

int main() {
  int a = 3;
  int b = 5;
  int c = 7;
  int d;
  d = (a>c||b>c);
  cout << d <<"\n";
  
  d = (a>b||b>c);
  cout << d <<"\n";
  
  d = (c>b&&b>a);
  cout << d <<"\n"
  
  d = (a<b&&b>c);
  cout << d <<"\n";
}

### Example - if

#include <iostream>
using namespace std;

int main() {
  cout << "Enter a number:";
  int number;
  cin >> number;
  if(number>=10) {
    cout << number;
  }
  return 0;
}

### Example - if else

#include <iostream>
using namespace std;

int main() {
  cout << "Enter your score:";
  int score;
  cin >> score;
  if(score>=60) {
    cout << "Pass" << endl;
  }
  else {
    cout << "Fail" << endl;
  }
  return 0;
}

### Exercise 7

<!-- :::spoiler **解答**

#include <iostream>
using namespace std;

int main() {
  float score;
  cout << "Enter your score";
  cin >> score;
  cout << "You get level ";
  if(score >= 90.0) {
    cout << "A";
  }
  else if(score >= 80.0) {
    cout << "B";
  }
  else if(score >= 70.0) {
    cout << "C";
  }
  else {
    cout << "F";
  }
  return 0;
}

::: -->

### Example - break in loop(for)

#include <iostream>
using namespace std;

int main() {
  int count = 0;
  for(int i = 10; i <= 40; i += 2) {
    count++;
    if(i % 8 == 0) {
      break;
    }
    cout << i << " ";
  }
  cout << "\n" << count;
  return 0;
}

### Example - break in loop(while)

#include <iostream>
using namespace std;

int main() {
  int count = 0;
  while(i<=40) {
    count++;
    if(i % 8 == 0) {
      break;
    }
    cout << i << " ";
    i += 2;
  }
  cout << "\n" << count;
  return 0;
}

### Example - continue in loop(while)

#include <iostream>
using namespace std;

int main() {
  int i = 0;
  while(i < 20) {
    i = i + 2;
    if(i == 10) {
      continue;
    }
    cout << i << " ";
  }
  return 0;
}

### Example - continue in loop(for)

#include <iostream>
using namespace std;

int main() {
  int i = 0;
  for(int i = 0; i < 20; i += 2) {
    if(i == 10) {
      continue;
    }
    cout << i << " ";
  }
  return 0;
}

### Exercise 8

<!-- :::spoiler **解答**

#include <iostream>
using namespace std;

int main() {
  for(int i = 1; i <= 10; i++) {
    cout << i << " ";
  }
  cout << "\n";
  for(int i = 10; i >= 1; i--) {
    cout << i << " ";
  }
  return 0;
}

::: -->

### Example - 雙層迴圈

#include <iostream>
using namespace std;

int main() {
  int i = 0;
  for(int i = 1; i <= 9; i ++) {
    for(int j = 1; j <= 9; j ++) {
      cout << i*j << " ";
    }
    cout << "i = " << i << " ";
    cout << endl;
  }
  return 0;
}

### Exercise 9

<!-- :::spoiler **解答**

#include <iostream>
using namespace std;

int main() {
  cout << "Enter the height: ";
  int height;
  cin >> height;
  for(int i = 1; i <= height; i++) {
    for(int j = 1; j <=i; j++) {
      cout << j << " ";
    }
    cout << "\n";
  }
  return 0;
}

::: -->

### Exercise 10

:::spoiler **Hint**

#include <iostream>
using namespace std;

int main() {
  cout << "Enter the size of rectangle: ";
  int a;
  cin >> a;
  for(int i = 1; i <= a; i++) {
    if(/*Finish yourself */){
      for(int j = 1; j <= a; j++) {
        cout << /*Finish yourself */;
      } 
    }
    else {
      for(int j = 1; j <= a; j++) {
        if(/*Finish yourself */) {
          cout << /*Finish yourself */;
        }
        else {
          cout << /*Finish yourself */;
        }
      }
    }
    cout << "\n";
  }
  return 0;
}

:::

<!-- :::spoiler **解答**

#include <iostream>
using namespace std;

int main() {
  cout << "Enter the size of rectangle: ";
  int a;
  cin >> a;
  for(int i = 1; i <= a; i++) {
    if(i == 1 || i == a){
      for(int j = 1; j <= a; j++) {
        cout << "*";
      } 
    }
    else {
      for(int j = 1; j <= a; j++) {
        if(j == 1 || j == a) {
          cout << "*";
        }
        else {
          cout << " ";
        }
      }
    }
    cout << "\n";
  }
  return 0;
}

::: -->

### Example - switch(1)

#include <iostream>
using namespace std;

int main() {
  int n = 1;
  switch(n) {
    case 1:
      cout << "可樂";
      break;
    case 2:
      cout << "雪碧";
      break;
    case 3:
      cout << "紅茶";
      break;
    default:
      cout << "無效";
  }
}

### Example - switch(2)

#include <iostream>
using namespace std;

int main() {
  int n = 1;
  switch(n) {
    case 1:
      cout << "可樂";
    case 2:
      cout << "雪碧";
    case 3:
      cout << "紅茶";
    default:
      cout << "無效";
  }
}

### Exercise 11

<!-- :::spoiler **解答**

#include <iostream>
using namespace std;

int main() {
  int x;
  cout << "輸入分數";
  cin >> x;
  x /= 10;
  switch(x) {
    case 10:
      cout << "Excellent";
      break;
    case 9:
      cout << "Excellent";
      break;
    case 8:
      cout << "perfect";
      break;
    case 7:
      cout << "good";
      break;
    default:
      cout << "OK";
  }
}

::: -->

### Example - Basic function

#include <iostream>
#include<string>
using namespace std;
int change(int a) {
  cout << a;
  a++;
  cout << a;
  return a;
}
int main() {
  int x = 1, ans;
  cout << x; 
  ans = change(x);
  cout << ans;
}

### Example - 全域變數與區域變數

#include <iostream>
#include<string>
using namespace std;
int change(int x) {
  cout << x;
  x++;
  cout << x;
  return x;
}
int main() {
  int x = 1, ans;
  cout << x; 
  ans = change(x);
  cout << ans;
}

### Exercise 12

<!-- :::spoiler **解答**

#include <iostream>
#include <string>
using namespace std;
int larger(int x, int y) {
  if(x > y) {
    retrun x;
  }
  return y;
}
int main() {
  int x, y, ans;
  cout << "Enter:" << endl;
  cin >> x >> y;
  ans = larger(x, y);
  cout << ans;
}

::: -->

### Exercise 13

:::spoiler **Hint**

#include <iostream>
#include <string>
using namespace std;
void reverse(int x) {
  for(int i = 0; i < 4; i++) {
    *****
    *****
  }
}
int main() {
  int x,;
  cin >> x;
  reverse(x);
}

:::

<!-- :::spoiler **解答**

#include <iostream>
#include <string>
using namespace std;
void reverse(int x) {
  for(int i = 0; i < 4; i++) {
    cout << x % 10;
    x /= 10;
  }
}
int main() {
  int x,;
  cin >> x;
  reverse(x);
}

::: -->