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  1. // Elaine Torrez                          CS1A                         Chapter 6, P.374, #15
  2. // *****************************************************************************************
  3. // *                                       POPULATION                                       *
  4. // *--------------------------------------------------------------------------------------- *
  5. // * This program calculates and displays the projected size of a population over a given   *
  6. // * number of years, based on the starting size, annual birth rate, and annual death rate. *
  7. // * The formula used to find the new population each year is:                              *
  8. // *                                                                                       *
  9. // *            N = P + (B * P) - (D * P)                                                   *
  10. // *                                                                                       *
  11. // * where N = new population, P = current population,                                      *
  12. // *       B = birth rate, and D = death rate.                                              *
  13. // *--------------------------------------------------------------------------------------- *
  14. // * INPUT                                                                                  *
  15. // *   startPop : starting population size (>= 2)                                           *
  16. // *   birthRate: annual birth rate (non-negative, as a decimal)                            *
  17. // *   deathRate: annual death rate (non-negative, as a decimal)                            *
  18. // *   years    : number of years to project (>= 1)                                         *
  19. // *--------------------------------------------------------------------------------------- *
  20. // * OUTPUT                                                                                 *
  21. // *   Displays the population size for each projected year.                                *
  22. // *****************************************************************************************
  23.  
  24. #include <iostream>
  25. #include <iomanip>
  26. #include <limits>  // for input validation
  27. using namespace std;
  28.  
  29. // ---------------- Function Prototype ----------------
  30. double calcPopulation(double prevPop, double birthRate, double deathRate);
  31.  
  32. // ---------------------- MAIN -------------------------
  33. int main()
  34. {
  35.     double startPop, birthRate, deathRate, newPop;
  36.     int years;
  37.  
  38.     cout << fixed << setprecision(0);
  39.  
  40.     // ---------------------- INPUT ----------------------
  41.     cout << "Enter the starting population size: ";
  42.     cin >> startPop;
  43.     while (cin.fail() || startPop < 2)
  44.     {
  45.         cin.clear();
  46.         cin.ignore(numeric_limits<streamsize>::max(), '\n');
  47.         cout << "ERROR: Starting population must be at least 2. Re-enter: ";
  48.         cin >> startPop;
  49.     }
  50.  
  51.     cout << "Enter the annual birth rate (as a decimal, e.g., 0.03 for 3%): ";
  52.     cin >> birthRate;
  53.     while (cin.fail() || birthRate < 0)
  54.     {
  55.         cin.clear();
  56.         cin.ignore(numeric_limits<streamsize>::max(), '\n');
  57.         cout << "ERROR: Birth rate cannot be negative. Re-enter: ";
  58.         cin >> birthRate;
  59.     }
  60.  
  61.     cout << "Enter the annual death rate (as a decimal, e.g., 0.01 for 1%): ";
  62.     cin >> deathRate;
  63.     while (cin.fail() || deathRate < 0)
  64.     {
  65.         cin.clear();
  66.         cin.ignore(numeric_limits<streamsize>::max(), '\n');
  67.         cout << "ERROR: Death rate cannot be negative. Re-enter: ";
  68.         cin >> deathRate;
  69.     }
  70.  
  71.     cout << "Enter the number of years to project: ";
  72.     cin >> years;
  73.     while (cin.fail() || years < 1)
  74.     {
  75.         cin.clear();
  76.         cin.ignore(numeric_limits<streamsize>::max(), '\n');
  77.         cout << "ERROR: Number of years must be at least 1. Re-enter: ";
  78.         cin >> years;
  79.     }
  80.  
  81.     // -------------------- PROCESSING -------------------
  82.     cout << "\nPopulation Projection:\n";
  83.     cout << "------------------------------\n";
  84.     newPop = startPop;
  85.  
  86.     for (int i = 1; i <= years; i++)
  87.     {
  88.         newPop = calcPopulation(newPop, birthRate, deathRate);
  89.         cout << "Year " << setw(2) << i << ": " << newPop << endl;
  90.     }
  91.  
  92.     return 0;
  93. }
  94.  
  95. // ---------------- Function Definition ----------------
  96. double calcPopulation(double prevPop, double birthRate, double deathRate)
  97. {
  98.     // Formula: N = P + (B * P) - (D * P)
  99.     return prevPop + (birthRate * prevPop) - (deathRate * prevPop);
  100. }
  101.  
Success #stdin #stdout 0.01s 5276KB
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stdin
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100
0.03
0.01
5
stdout
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Enter the starting population size: Enter the annual birth rate (as a decimal, e.g., 0.03 for 3%): Enter the annual death rate (as a decimal, e.g., 0.01 for 1%): Enter the number of years to project: 
Population Projection:
------------------------------
Year  1: 102
Year  2: 104
Year  3: 106
Year  4: 108
Year  5: 110
https://ideone.com/Qkpq0z
language:
C++ (gcc 8.3)
created:
16 days ago
visibility:
public

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