We will use `__COUNTER__` and a `#define`, so it would eventually duplicates given parameter `N` times. I can't give you a macro that just `REPEAT(100, abcd)` and will expand to 100*abcd without defining 100 lines of macro. If you don't want to see how it works, scroll down to the bottom.↵
↵
Firstly, let's see this technique:↵
↵
```cpp↵
#define EXP(...) EXP1(EXP1(EXP1(EXP1(__VA_ARGS__))))↵
#define EXP1(...) EXP2(EXP2(EXP2(EXP2(__VA_ARGS__))))↵
#define EXP2(...) EXP3(EXP3(EXP3(EXP3(__VA_ARGS__))))↵
#define EXP3(...) EXP4(EXP4(EXP4(EXP4(__VA_ARGS__))))↵
#define EXP4(...) __VA_ARGS__ // Just expand it lots of times.↵
↵
#define REP() 1 DEFER(REP_I)()()↵
#define EMPTY()↵
#define DEFER(...) __VA_ARGS__ EMPTY()↵
#define REP_I() REP↵
↵
EXP(REP())↵
↵
```↵
↵
If you expand the `EXP(REP())`, you will see a lot of 1. Why? Because the macro `DEFER()` make it so that `REP` can be expanded many times within a single macro. Just like `void dfs() { cout << 1; dfs();}`. But this also has an end: it depends on how many time you expand it. That's why we added lots of `EXP()`. You can even add EXP5 and more, but you'll probably start lagging. Also you can try expand it for 1 or 2 times to see the difference.↵
↵
Also that's how the `SP()` macro made in my template.↵
↵
But how to make it stop? We can use `__COUNTER__`. After certain times of expansion, the `__COUNTER__` will reach a certain value, then we can make it stop.↵
↵
```cpp↵
#include <bits/stdc++.h>↵
using namespace std;↵
#define EXP(...) EXP1(EXP1(EXP1(EXP1(__VA_ARGS__))))↵
#define EXP1(...) EXP2(EXP2(EXP2(EXP2(__VA_ARGS__))))↵
#define EXP2(...) EXP3(EXP3(EXP3(EXP3(__VA_ARGS__))))↵
#define EXP3(...) EXP4(EXP4(EXP4(EXP4(__VA_ARGS__))))↵
#define EXP4(...) __VA_ARGS__↵
↵
#define EMPTY(...)↵
#define DEFER(...) __VA_ARGS__ EMPTY()↵
#define CONCAT(A, B) CCONCAT(A, B)↵
#define CCONCAT(A, B) A##B↵
#define SECO(A, B, ...) B↵
#define BASE(B) , DEFER(REP_I)()(__COUNTER__, B)↵
#define REP(A, B) B DEFER(SECO)(CONCAT(REP_, A), BASE)(B)↵
#define REP_I() REP↵
↵
#define rep(A) EXP(REP(__COUNTER__, A))↵
↵
#define REP_29 A, EMPTY↵
#define REP_59 A, EMPTY↵
#define REP_99 A, EMPTY↵
↵
int a[]{rep(1)};↵
int b[]{rep(1)};↵
int c[]{rep(3)};↵
↵
int main()↵
{↵
cout << size(a) << endl; // 30↵
cout << size(b) << endl; // 30↵
cout << size(c); // 40↵
}↵
↵
```↵
↵
To use this, assume current `__COUNTER__` value is x, then `#define REP_X+N-1 A, EMPTY`, so the given macro A will expand N times. Then x will add N.↵
↵
To customize separator, see the part: `#define BASE(B) ,` and change the comma to anything else.↵
↵
If you see it expand to something else at the end, you need to add more `EXP`. Currently it can repeat at most 171 times using one `rep`. Change `REP_99` to `REP_230` and `REP_231` to see.
↵
Firstly, let's see this technique:↵
↵
```cpp↵
#define EXP(...) EXP1(EXP1(EXP1(EXP1(__VA_ARGS__))))↵
#define EXP1(...) EXP2(EXP2(EXP2(EXP2(__VA_ARGS__))))↵
#define EXP2(...) EXP3(EXP3(EXP3(EXP3(__VA_ARGS__))))↵
#define EXP3(...) EXP4(EXP4(EXP4(EXP4(__VA_ARGS__))))↵
#define EXP4(...) __VA_ARGS__ // Just expand it lots of times.↵
↵
#define REP() 1 DEFER(REP_I)()()↵
#define EMPTY()↵
#define DEFER(...) __VA_ARGS__ EMPTY()↵
#define REP_I() REP↵
↵
EXP(REP())↵
↵
```↵
↵
If you expand the `EXP(REP())`, you will see a lot of 1. Why? Because the macro `DEFER()` make it so that `REP` can be expanded many times within a single macro. Just like `void dfs() { cout << 1; dfs();}`. But this also has an end: it depends on how many time you expand it. That's why we added lots of `EXP()`. You can even add EXP5 and more, but you'll probably start lagging. Also you can try expand it for 1 or 2 times to see the difference.↵
↵
Also that's how the `SP()` macro made in my template.↵
↵
But how to make it stop? We can use `__COUNTER__`. After certain times of expansion, the `__COUNTER__` will reach a certain value, then we can make it stop.↵
↵
```cpp↵
#include <bits/stdc++.h>↵
using namespace std;↵
#define EXP(...) EXP1(EXP1(EXP1(EXP1(__VA_ARGS__))))↵
#define EXP1(...) EXP2(EXP2(EXP2(EXP2(__VA_ARGS__))))↵
#define EXP2(...) EXP3(EXP3(EXP3(EXP3(__VA_ARGS__))))↵
#define EXP3(...) EXP4(EXP4(EXP4(EXP4(__VA_ARGS__))))↵
#define EXP4(...) __VA_ARGS__↵
↵
#define EMPTY(...)↵
#define DEFER(...) __VA_ARGS__ EMPTY()↵
#define CONCAT(A, B) CCONCAT(A, B)↵
#define CCONCAT(A, B) A##B↵
#define SECO(A, B, ...) B↵
#define BASE(B) , DEFER(REP_I)()(__COUNTER__, B)↵
#define REP(A, B) B DEFER(SECO)(CONCAT(REP_, A), BASE)(B)↵
#define REP_I() REP↵
↵
#define rep(A) EXP(REP(__COUNTER__, A))↵
↵
#define REP_29 A, EMPTY↵
#define REP_59 A, EMPTY↵
#define REP_99 A, EMPTY↵
↵
int a[]{rep(1)};↵
int b[]{rep(1)};↵
int c[]{rep(3)};↵
↵
int main()↵
{↵
cout << size(a) << endl; // 30↵
cout << size(b) << endl; // 30↵
cout << size(c); // 40↵
}↵
↵
```↵
↵
To use this, assume current `__COUNTER__` value is x, then `#define REP_X+N-1 A, EMPTY`, so the given macro A will expand N times. Then x will add N.↵
↵
To customize separator, see the part: `#define BASE(B) ,` and change the comma to anything else.↵
↵
If you see it expand to something else at the end, you need to add more `EXP`. Currently it can repeat at most 171 times using one `rep`. Change `REP_99` to `REP_230` and `REP_231` to see.
