编写程序计算Fibonacci数列的前x项

以下是一个计算Fibonacci数列前x项和的C++程序示例：

#include <iostream>
using namespace std;

int fbi(int n) {
    if (n <= 0)
        return 0;
    if (n == 1 || n == 2)
        return 1;
    int a = 1, b = 1, c;
    for (int i = 3; i <= n; i++) {
        c = a + b;
        a = b;
        b = c;
    }
    return b;
}

int sum_fbi(int x) {
    if (x <= 0)
        return 0;
    int s = 0;
    for (int i = 1; i <= x; i++) {
        s += fbi(i);
    }
    return s;
}

int main() {
    int x = 6;
    cout << "斐波那契数列前15项为:";
    for (int i = 1; i <= 15; i++) {
        cout << " " << fbi(i);
    }
    cout << endl;
    cout << "斐波那契数列前" << x << "项和为" << sum_fbi(x) << endl;
    system("pause");
    return 0;
}