我可以设置例如array [n + k] = array [0]吗？

Question

If I have this code:

#include <iostream>

using namespace std;

int main()
{
    int n, i;
    cin >> n;
    float array10[n];
    cin >> array10[i];
}

How can I create array10[n+1] and set the value of array10[0] ?

Answer 1

You can't. In fact, array10[n]; isn't legal C++ (even if n was initialized). Variable length arrays aren't a C++ feature.

Use std::vector :

cin >> n;
std::vector<int> vec(n);
cin >> vec[i];

Answer 2

This code

int n, i;
float array10[n];

is invalid because arrays in C+ require that their sizes would be constant expressions at compile time. (Though some compilers have its own language extensions that allow to do that. But this code does not satisfy the C++ Standard) And if an array is defined you may not change its size. If n would be a constant expression then you could write for example

const int n = 10;
float array[n];
float array1[n + 1]

Otherwise you have two approaches. Either you should use standard C++ container std::vector

For example

int n = 10;
std::vector<float> v( n );

and then you can resize this vector

v.resize( n + 1 );

Or you should dynamically allocate an array. For example

int n = 10;
float *array = new float[n];

and then reallocate it;

float *tmp = new float[n + 1];

std::copy( array, array + n, tmp );
delete []array;
array = tmp;

Answer 3

You can do it by declaring array10 as a pointer

cin >> n;
float* array10 = new float[n];
cin >> array10[i];
//do something
delete[] array10;