CODEWITHSUNDEEP
c++arraysrandomshuffle
blackseed32
blackseed32

Reputation: 1

How to make an array to not repeat?

Here is my code for a simple game. paste it and try it.

#include <iostream>
#include <string>
#include <ctime>
#include <cstdlib>
using namespace std;

int main (void)
{
    string  g[4],
    b[4],
    a[4],
    l[4];

    srand((unsigned int)time(0));

    cout << "Welcome!\n\n";
    cout << "Type 4 girl names.\n";
    for (int gi = 0; gi < 4; gi++) 
        cin >> g[gi];

    cout << "Type 4 boy names.\n";
    for (int bi = 0; bi < 4; bi++)
        cin >> b[bi];

    cout << "\nWhat they do (enter 4 actions)?\n";
    for (int ai = 0; ai < 4; ai++)
        getline(cin, a[ai]);

    cout << "\nWhere is happening (enter 4 locations)?\n";
    for (int li = 0; li < 4; li++)
        getline(cin, l[li]);

    for (int c = 0; c < 4; c++)
        cout << g[rand() % 4] << " and " << b[rand() % 4] << " are " << a[rand() %     4] << " from a " << l[rand() % 4] << endl;

    return (0);
}

At the end in the 4 lines some of the names, actions and locations repeat. How do I make them to not repeat and use every name that you will enter?

Upvotes: 0

Views: 793

Answers (2)

Lightness Races in Orbit
Lightness Races in Orbit

Reputation: 385144

for (int c = 0; c < 4; c++)
    cout << g[rand() % 4] << " and " << b[rand() % 4] << " are "
         << a[rand() %     4] << " from a " << l[rand() % 4] << endl;

You've made an assumption that consecutive calls to rand() are guaranteed to not yield the same result as previous calls to rand(), but this is baseless.

Thus, there is always a possibility that you will get repeats; in fact, there is a 1 in 64 chance that you will get the same answer each time.

Either remove the randomness, or perform a random array shuffle before the loop (as demonstrated by Mr @Eladidan). Or, create an array of the numbers 0,1,2,3, shuffle that, then use it as indexes into your data arrays.

It's the nature of random shuffling (rather than random extraction) that'll give you a non-repeating answer.

Upvotes: 0

eladidan
eladidan

Reputation: 2644

Use std::random_shuffle:

std::random_shuffle(g, g + 4);
std::random_shuffle(b, b + 4);
std::random_shuffle(a, a + 4);
std::random_shuffle(l, l + 4);

And then just iterate over all of the shuffled arrays:

for (int c = 0; c < 4; c++)
    cout << g[c] << " and " << b[c] << " are " << a[c] << " from a " << l[c] << endl;

Upvotes: 1

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