※ 引述《red0whale (red whale)》之銘言：
: 剛才做題目，
: https://i.imgur.com/NI4TYj5.jpg
: 九九乘法表用兩個或一個迴圈來做我都會
: 但不用迴圈叫我列九九乘法表是哪招？
: 難道是要我直接從1*1列到9*9嗎？
: 還是其實有妙招？
: 說實在我真想不到不用迴圈就能簡單列出九九乘法表的方法了
我覺得這題要求用 C 真的比較困難，C++ 的話可以輕鬆很多
大概像這樣 https://ideone.com/Yb0TqG
#include <iomanip>
#include <iostream>
template<int...> struct IntegerSequence {
};
template<int n, class = IntegerSequence<>, bool = n == 0>
struct MakeIntegerSequenceImpl;
template<int n, int... i>
struct MakeIntegerSequenceImpl<n, IntegerSequence<i...>, true> {
typedef IntegerSequence<i...> type;
};
template<int n, int... i>
struct MakeIntegerSequenceImpl<n, IntegerSequence<i...>, false> {
typedef typename MakeIntegerSequenceImpl<
n - 1, IntegerSequence<n - 1, i...>>::type type;
};
template<int n>
using MakeIntegerSequence = typename MakeIntegerSequenceImpl<n>::type;
template<int n>
struct MultiplicationTableCell {
static constexpr int value = ((n / 9) + 1) * ((n % 9) + 1);
};
template<class> struct MultiplicationTableImpl;
template<int... n>
struct MultiplicationTableImpl<IntegerSequence<n...>> {
static const int value[];
};
template<int... n>
const int MultiplicationTableImpl<IntegerSequence<n...>>::value[] = {
MultiplicationTableCell<n>::value...
};
struct MultiplicationTable :
MultiplicationTableImpl<MakeIntegerSequence<81>> {
static void print_twoLoops() {
for (int i = 0; i < 9; ++i) {
for (int j = 0; j < 9; ++j) {
std::cout << std::setw(2) << value[(i * 9) + j] << ',';
}
std::cout << std::endl;
}
}
static void print_oneLoop() {
for (int i = 0; i < 81; ++i) {
std::cout << std::setw(2) << value[i] << ',';
if ((i % 9) == 8) {
std::cout << std::endl;
}
}
}
static void print_noLoop_twoArgs(int i = 0, int j = 0) {
if (i == 9) {
return;
}
if (j == 9) {
std::cout << std::endl;
return print_noLoop_twoArgs(i + 1, 0);
}
std::cout << std::setw(2) << value[(i * 9) + j] << ',';
print_noLoop_twoArgs(i, j + 1);
}
static void print_noLoop_oneArg(int i = 0) {
if (i == 81) {
return;
}
std::cout << std::setw(2) << value[i] << ',';
if ((i % 9) == 8) {
std::cout << std::endl;
}
print_noLoop_oneArg(i + 1);
}
};
int main() {
std::cout << "Use 'two' for loops:" << std::endl;
MultiplicationTable::print_twoLoops();
std::cout << std::endl;
std::cout << "Use 'only one' for loop:" << std::endl;
MultiplicationTable::print_oneLoop();
std::cout << std::endl;
std::cout << "Use 'no loops' (two arguments):" << std::endl;
MultiplicationTable::print_noLoop_twoArgs();
std::cout << std::endl;
std::cout << "Use 'no loops' (one argument):" << std::endl;
MultiplicationTable::print_noLoop_oneArg();
return 0;
}