8、C++编程实现函数fun的功能是：查找字符串str中值为x的元素，返回找到值为x的元素个数，并把这些值为x的下标依次保存在数组bb中。

以下是C++编程实现函数fun的功能的示例代码：

#include <iostream>
using namespace std;

int fun(char* str, char x, int* bb) {
    int count = 0;
    int index = 0;
    
    for (int i = 0; str[i] != '\0'; i++) {
        if (str[i] == x) {
            count++;
            bb[index] = i;
            index++;
        }
    }
    
    return count;
}

int main() {
    char str[] = "Hello World";
    char x = 'o';
    int bb[100];
    
    int count = fun(str, x, bb);
    
    cout << "Number of elements with value " << x << ": " << count << endl;
    cout << "Indices of elements with value " << x << ": ";
    for (int i = 0; i < count; i++) {
        cout << bb[i] << " ";
    }
    cout << endl;
    
    return 0;
}

输出结果为：

Number of elements with value o: 2
Indices of elements with value o: 4 7