Function Pointers
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#include <iostream>
#include <vector>
#include <cmath> // For pow().
using namespace std;
const int YEARS = 20;
const double INTEREST_RATE = 0.07;
/**
* Applies a given function, `func`, to each element of the list, `numbers`, and
* returns a list of results in the same order.
*/
vector<double> map(vector<double> numbers, double (*func)(double)) {
vector<double> result(numbers.size());
for (int i = 0; i < numbers.size(); i++) {
result[i] = func(numbers[i]);
}
return result;
}
/**
* Returns the amount compounded annually at the given interest rate for the
* given number of years, when provided an initial quantity, `principal`.
*/
double compound_interest(double principal) {
return principal * pow(1 + INTEREST_RATE, YEARS);
}
/**
* Returns the number of years until a person with the given income (and no
* expenses) becomes a millionaire, taking investment returns into account.
*/
double years_until_millionaire(double n) {
int years = 0;
double money = 0;
while (true) {
++years;
money += n;
money = money * (1 + INTEREST_RATE);
if (money > 1000000) {
return years;
}
}
}
double print_element(double n) {
cout << n << ",\t";
return 0;
}
double times_a_thousand(double n) {
return 1000 * n;
}
int main() {
double (*func)(double) = times_a_thousand;
cout << func(4) << endl << endl;
vector<double> salaries = {56, 84, 117, 145, 211};
vector<double> salaries_k = map(salaries, times_a_thousand);
cout << "Initial:\t";
map(salaries_k, print_element);
cout << endl;
cout << YEARS << " years at " << 100 * INTEREST_RATE << "%:\t";
vector<double> compounded_money = map(salaries_k, compound_interest);
map(compounded_money, print_element);
cout << endl;
cout << "Millionaire:\t";
vector<double> years = map(salaries_k, years_until_millionaire);
map(years, print_element);
cout << endl;
return 0;
}
Cpp
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