Non-repeating random numbers - c++

Question

I'm working on a synonym puzzle, it gives you a word and wants you to find the synonym of it given the lenght of the word. Everything works fine, but it happens on an ordered sequence; words do not appear randomly. I need knumber of non-repeating random numbers for that. Here's my code:
#include<iostream>
#include<string>
#include<cstdlib>
#include<ctime>
using namespace std;
int main()
{
const int k=4;
string word[k]={"furious","tiny","untrue", "humorous", "harm"};
string nword[k]={"angry","small","false", "funny", "damage"};
string j;
int point, p = 0;
int ctr=0;
srand(time(NULL));
int randNum = (rand() % k) + 0;
for(int i=0; i<k; i++)
{
cout << nword[i] << "\n";
cout << "The length of the word: " << word[i].length() << "\n";
cin>>j;
ctr++;
if(j==word[i])
{
cout<<"Correct! Score: " << i+1 << " point." << "\n\n";
}
else
{
cout<<"Wrong"<<endl;
}
}
return 0;
}
As you can see, the variable randNum holds the value of the random number from 0 to k, (k is 4, combined with 0, I got 5 words). In for loop, when I set the nword and word like nword[randNum], and word[randNum], the result leaves a lot to be desired. First, I think there's no sync for the two (nword and word). It will apply different random numbers for the two (I might be wrong) and the second, it will be repetitive. As seen, the execution is score-based and completable, so I need non repeating questions until it reaches to k.

Answer 1

You could shuffle your word arrays by using the Durstenfeld shuffle:
for(int i=k-1; i>0; i--)
{
int j = rand() % (i+1)
string temp = word[i];
word[i] = word[j];
word[j] = temp;
temp = nword[i];
nword[i] = nword[j];
nword[j] = temp;
}
As pointed out by WhozCraig, an alternative option (arguably better, as it doesn't require permuting multiple arrays), is to create an array with indices 0..(k-1) and shuffle this array instead. This array would then contain a set of randomised indices which could be used to iterate over your word arrays.
#include <iostream>
#include <algorithm>
#include <string>
#include <random>
#include <numeric>
using namespace std;
int main()
{
static const size_t k=5;
string word[k]={"furious","tiny","untrue", "humorous", "harm"};
string nword[k]={"angry","small","false", "funny", "damage"};
int ctr=0;
// build prng
std::random_device rd;
std::mt19937 rng(rd());
// build index sequence, then shuffle
size_t idx[k];
std::iota(std::begin(idx), std::end(idx), 0);
std::shuffle(std::begin(idx), std::end(idx), rng);
for(auto i : idx)
{
std::string s;
cout << nword[i] << "\n";
cout << "The length of the word: " << word[i].length() << "\n";
if (!(cin>>s))
break;
if(s==word[i])
{
cout<<"Correct! ";
++ctr;
}
else
{
cout<<"Wrong. ";
}
std::cout << "Score: " << ctr << " point(s).\n\n";
}
return 0;
}