Shuffling vectors in C++ - c++

Question

I am working on a programme which takes an initial vector as an inpit.This vector is vector of size 20.The programme then generates 10 random vectors from this vector.For this purpose I choose 2 ransom indices in the initial vector and swap them with each other to generate a new vector.This is done to generate all the 10 new vectors.
The 10 new vectors generated should be stored in the following 2 dimensional vector
vector<vector<int>> allparents
I have been able to generate 2 random indice numbers using the srand() function and then swap the elements at these indices for the initial vector.However I am unable to generate 10 of such random parents and then store them in the allparents 2D vector.My code is as follows :
#include<vector>
#include<iostream>
#include<algorithm>
#include<cstdio>
#include<ctime>
using namespace std;
int main () {
srand(time(NULL));
int i1=(rand()%19+1);
int i2=(rand()%19+1);
cout<<i1<<endl;
cout<<i2<<endl;
vector<int> initial={71,127,428,475,164,253,229,395,92,189,41,110,443,490,278,305,28,58,371,560};
vector<vector<int>> allparents;
for(int r=0;r<10;r++){
for(int c=0;c<20;c++){
swap(initial[i1],initial[i2]);
allparents[r][c]=initial[c];
cout<<allparents[r][c]<" "<<endl;
}
}
return 0;
}
As I am new to vectors,I would request your help in this programme.Thanks.

Answer 1

First of all, I would not say that you're "generating random vectors", you're just shuffling a predefined one.
Second, I suggest to create small working functions and assemble your program with those:
vector<int> shuffle(vector<int> v) {
// Use the implementation you want here, I will use a std algorithm
static auto rng = std::default_random_engine {};
std::shuffle(std::begin(v), std::end(v), rng);
return v; // this is a copy of the vector
}
int main() {
vector<int> initial= {
71,127,428,475,164,253,229,395,92,189,41,110,443,490,278,305,28,58,371,560
};
// Generate 10 shuffled vectors
vector<vector<int>> shuffledVectors;
for (int i = 0; i < 10; i++) {
vector<int> shuffled = shuffle(initial);
shuffledVectors.push_back(shuffled);
}
// Print them
for (vector<int>& v : shuffledVectors) {
for (int& i : v)
cout << i << " ";
cout << endl;
}
return 0;
}
Output:
164 41 110 305 278 28 58 127 229 189 475 395 560 428 71 443 253 371 490 92
490 71 305 58 428 127 28 110 92 443 189 229 278 475 371 395 560 41 253 164
395 278 560 490 28 164 71 229 58 41 428 305 127 253 475 371 92 189 110 443
164 475 92 253 229 189 127 560 71 58 41 443 428 395 371 490 110 278 28 305
443 253 428 110 278 71 475 127 58 41 371 229 305 189 395 164 28 490 92 560
560 28 58 71 229 41 490 475 189 443 253 395 305 164 371 278 428 92 110 127
395 443 371 58 253 305 92 127 475 110 428 229 189 41 164 278 71 560 28 490
278 189 71 127 443 110 28 428 305 560 371 58 229 253 395 164 41 490 475 92
28 395 92 443 560 278 371 71 58 305 475 253 428 490 229 189 164 110 41 127
443 71 428 229 127 278 490 58 475 253 164 110 92 189 395 560 305 41 28 371