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  1. #include <iostream>
  2. using namespace std;
  3.  
  4. struct Diem {
  5.     int x, y;
  6. };
  7.  
  8. class Bai2 {
  9. private:
  10.     Diem* arr;
  11.     int sl;
  12. public:
  13.     ~Bai2() {
  14.         delete[] arr;
  15.         sl = 0;
  16.         arr = nullptr;
  17.     }
  18.     Bai2(int s = 0) {
  19.         sl = s;
  20.         arr = new Diem[sl];
  21.     }
  22.     void Nhap() {
  23.         cin >> sl;
  24.         arr = new Diem[sl];
  25.         for (int i = 0; i < sl; i++) {
  26.             cin >> arr[i].x >> arr[i].y;
  27.         }
  28.     }
  29.     void Xuat() {
  30.         for (int i = 0; i < sl; i++) {
  31.             cout << "(" << arr[i].x << "," << arr[i].y << ")" << "\n";
  32.         }
  33.     }
  34.     void DienTich_XacDinhChieu() {
  35.         double tong = 0;
  36.         for (int i = 0; i < sl; i++) {
  37.             if (i + 1 == sl) tong += arr[i].x * arr[0].y - arr[0].x * arr[i].y;
  38.             else tong += arr[i].x * arr[i + 1].y - arr[i + 1].x * arr[i].y;
  39.         }
  40.         cout << "Dien tich da giac: " << 0.5 * abs(tong) << "\n";
  41.         if (tong > 0) cout << "Chieu cua da giac là chieu nguoc chieu kim dong ho!\n";
  42.         else cout << "Chieu cua da giac là chieu cung chieu kim dong ho!\n";
  43.     }
  44.     void LoiHayLom() {
  45.         bool duong = false;
  46.         bool am = false;
  47.         for (int i = 0; i < sl; i++) {
  48.             Diem p1 = arr[(i - 1 + sl) % sl];
  49.             Diem p2 = arr[i];
  50.             Diem p3 = arr[(i + 1) % sl];
  51.             int vectorX1 = p2.x - p1.x;
  52.             int vectorY1 = p2.y - p1.y;
  53.             int vectorX2 = p3.x - p2.x;
  54.             int vectorY2 = p3.y - p2.y;
  55.             int tch = vectorX1 * vectorY2 - vectorX2 * vectorY1;
  56.             if (tch < 0) am = true;
  57.             if (tch > 0) duong = true;
  58.         }
  59.         if (duong && am) cout << "Da giac nay la da giac lom!\n";
  60.         else cout << "Da giac nay la da giac loi!\n";
  61.     }
  62. };
  63.  
  64. int main() {
  65.     Bai2 a;
  66.     a.Nhap();
  67.     a.Xuat();
  68.     a.DienTich_XacDinhChieu();
  69.     a.LoiHayLom();
  70.     return 0;
  71. }
Success #stdin #stdout 0s 5324KB
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stdin
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Standard input is empty
stdout
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Dien tich da giac: 0
Chieu cua da giac là chieu cung chieu kim dong ho!
Da giac nay la da giac loi!
https://ideone.com/9X2rVA
Lời giải Bài 2
language:
C++ (gcc 8.3)
created:
1 day ago
visibility:
public

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