C++迭代

Question

比方說，我有這樣的數組：

int oldv[10] = {16, 12, 24, 96, 45, 22, 18, 63, 47, 56}; 

，另一種像

int newv[8]; 

，我想從直到的old交替兩端填寫新某些條件滿足，我會有：

newv = [16, 56, 12, 47, 24, 63 ...] 

比方說，我想只把新的3個號碼取自舊的（即：16,56,12）。 我已經嘗試用下面的循環，但當然是不夠的...

for(int i = 0; i < 3; i++) 
    newv[i] = oldv[i*(sizeof(oldv)-1)]; 

任何幫助嗎？

Answer 1

int _old[10] = {16, 12, 24, 96, 45, 22, 18, 63, 47, 56}; 
int _new[8]; 

const int old_size = sizeof(_old)/sizeof(int); 
const int new_size = sizeof(_new)/sizeof(int); 

for (int i = 0; i < new_size; ++i) 
{ 
    if (i % 2) 
     _new[i] = _old[old_size - i/2 - 1]; 
    else 
     _new[i] = _old[i/2]; 

    std::cout << _new[i] << " "; 
} 

std::cout << std::endl; 

返回16 56 12 47 24 63 96 18

See it live

Answer 2

享受。

#include <algorithm> 
#include <iostream> 
#include <iterator> 

using namespace std; 

int main(int, char**) 
{ 
    int oldv[] = { 16, 12, 24, 96, 45, 22, 18, 63, 47, 56 }; 
    int newv[8]; 
    size_t numbers_i_want = 3; 

    size_t oldv_b = 0; 
    size_t oldv_e = sizeof oldv/sizeof *oldv; 
    size_t newv_e = sizeof newv/sizeof *newv; 

    for(size_t i = 0; 
     i != min(numbers_i_want, newv_e) && oldv_b != oldv_e; 
     ++i) 
    { 
     newv[i] = (i % 2) ? oldv[--oldv_e] : oldv[oldv_b++]; 
    } 

    copy(newv, newv + min(numbers_i_want, newv_e), 
     ostream_iterator<decltype(*newv)>(cout, " ")); 
    return 0; 
}