can not swap array elements c++

Question

I am new to C++. I am trying to solve a problem in the textbook: swap the first and last element in an array. But when I run the code I wrote, nothing happened and even the sentence "Please enter the numbers in the array: " does not show up. Anyone could give some help? Thanks.

#include <iostream>

using namespace std;

int swap(int values[], int size)
{
    int temp = values[0];
    values[0] = values[size-1];
    values[size-1] = temp;
}

int main()
{
    const int SIZE = 5;
    int test[SIZE];
    cout << "Please enter the numbers in the array: " << endl;
    int input;
    cin >> input;
    for(int i=0; i<SIZE; i++)
    {
            test[i] = input;
    }
    swap(test, SIZE);
    cout << test[SIZE] << endl;
    return 0;
}

There are some output on Wandbox. Anyway, cout << test[SIZE] << endl; acccess out of bounds and it is bad. — MikeCAT
– MikeCAT, Commented Oct 1, 2015 at 15:05
swap() has a return type other than void but does not return anything. — bku_drytt
– bku_drytt, Commented Oct 1, 2015 at 15:11
Moreover, you fill the array with the same single input value in all cells. Swaping the cells yield no visible result. — CygnusX1
– CygnusX1, Commented Oct 1, 2015 at 15:13
Are you aware that the name swap already exists in namespace std, which you're bringing into the global scope with your using namespace std;? It won't cause problems here because overload resolution picks your function, but you'll run into clashes in future if you insist on using namespace std. — Andrew
– Andrew, Commented Oct 1, 2015 at 15:26
It is an anti-pattern and a bad habit to use constants in UPPERCASE (unless it is a preprocessor macro), please avoid that. — Slava
– Slava, Commented Oct 1, 2015 at 15:28

Toby Speight · Accepted Answer · 2015-10-01 15:55:36Z

1

There were a few mistakes:

You should get the input inside the loop and then assign it to the test array.
When printing the swapped value, access the test array with SIZE-1 instead of SIZE, because array indexes run from 0 to SIZE-1, inclusive.

You declared swap() as returning int, but provided no return statement (this suggests that you haven't enabled enough warnings from your compiler).

#include <iostream>

using namespace std;

void swap(int values[], int size)
{
    int temp = values[0];
    values[0] = values[size-1];
    values[size-1] = temp;
}

int main()
{
    const int SIZE = 5;
    int test[SIZE];
    int input;
    cout << "Please enter the numbers in the array: " << endl;

    for(int i=0; i<SIZE; i++)
    {
            cin >> input;
            test[i] = input;
    }
    swap(test, SIZE);
    cout << test[SIZE-1] << endl;
    return 0;
}

edited Oct 1, 2015 at 15:55

Toby Speight

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answered Oct 1, 2015 at 15:43

user3320657

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Comments

ciamej · Accepted Answer · 2015-10-01 16:09:04Z

1

#include <iostream>

using namespace std;

//Here return type should be void as you are not returning value.
void swap(int values[], int size)
{
   int temp = values[0];
   values[0] = values[size-1];
   values[size-1] = temp;
}

int main()
{
   const int SIZE = 5;
   int test[SIZE];
   cout << "Please enter the numbers in the array: " << endl;

   //USE LOOP TO TAKE INPUT ONE BY ONE IN AN ARRAY
   for(int i = 0; i < SIZE; i++)
    cin >> test[i];

   swap(test, SIZE);

   //USE LOOP TO DISPLAY ELEMENT ONE BY ONE
   for(int i = 0; i < SIZE; i++)
     cout << test[i] << endl;

   return 0;
}

edited Oct 1, 2015 at 16:09

ciamej

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answered Oct 1, 2015 at 15:23

cryptomanic

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2 Comments

Andrew Over a year ago

Perhaps size instead of SIZE? ALL-CAPS identifiers are best reserved for macros.

Jarod42 Over a year ago

And in C++11: for(auto& e : test) std::cin >> e; swap(test, SIZE); for(auto e : test) std::cout << e << std::endl;

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