C ++阵列复制/移位

Question

We had a project that asked us to Write a program that allows a user to enter a series of numbers "read numbers into an array for further processing, user signals that they are finished by entering a negative number (negative not used in calculations), after all numbers have been read in do the following, sum up the #'s entered, count the #'s entered, find min/max # entered, compute average, then output them on the screen. So the working version of this that I made looks like so

/* Reads data into array.  
paramater a = the array to fill
paramater a_capacity = maximum size  
paramater a_size = filled with size of a after reading input. */

void read_data(double a[], int a_capacity, int& a_size)
{
    a_size = 0;

bool computation = true;

while (computation)
{
    double x;
    cin >> x;

    if (x < 0)
        computation = false;

    else if (a_size == a_capacity)
    {
        cout << "Extra data ignored\n";
        computation = false;
    }
    else
    {
        a[a_size] = x;
        a_size++;
    }
}
} 


/* computes the maximum value in array
paramater a = the array
Paramater a_size = the number of values in a */

double largest_value(const double a[], int a_size)
{
if(a_size < 0)
    return 0;

double maximum = a[0];

for(int i = 1; i < a_size; i++)
    if (a[i] > maximum)
        maximum = a[i];
return maximum;

}


/* computes the minimum value in array */
double smallest_value(const double a[], int a_size)
{
if(a_size < 0)
    return 0;

double minimum = a[0];

for(int i = 1; i < a_size; i++)
    if (a[i] < minimum)
        minimum = a[i];
return minimum;
}

//computes the sum of the numbers entered
double sum_value(const double a [], int a_size)
{   
if (a_size < 0)
    return 0;

double sum = 0;

for(int i = 0; i < a_size; i++)
    sum = sum + a[i];
return sum;
}

//keeps running count of numbers entered 
double count_value(const double a[], int a_size)
{
if (a_size < 0)
    return 0;

int count = 0;
for(int i = 1; i <= a_size; i++)
    count = i;
return count;

}



int _tmain(int argc, _TCHAR* argv[])
{

const int INPUT_CAPACITY = 100;
double user_input[INPUT_CAPACITY];
int input_size = 0;
double average = 0;

cout << "Enter numbers.  Input negative to quit.:\n";

read_data(user_input, INPUT_CAPACITY, input_size);

double max_output = largest_value(user_input, input_size);
cout << "The maximum value entered was " << max_output << "\n";

double min_output = smallest_value(user_input, input_size);
cout << "The lowest value entered was " << min_output << "\n";

double sum_output = sum_value(user_input, input_size);
cout << "The sum of the value's entered is " << sum_output << "\n";

double count_output = count_value(user_input, input_size);
cout << "You entered " << count_output << " numbers." << "\n";

cout << "The average of your numbers is  " << sum_output / count_output << "\n";




string str;

getline(cin,str);
getline(cin,str);


return 0;
}

That went fine, the problem I am having now is part 2. Where we are to "copy the array to another and shift an array by N elements". I'm not sure where to begin on either of these. I've looked up a few resources on copying array's but I was not sure how to implement them in the current code I have finished, especially when it comes to shifting. If anyone has any thoughts, ideas, or resources that can help me on the right path it would be greatly appreciated. I should point out as well, that I am a beginner (and this is a beginners class) so this assignment might not be the 'optimal' way things could be done, but instead incorporates what we have learned if that makes sense.

Answer 1

for(int i = 0; i < n; ++i){
    int j = (i - k)%n;
    b[i] = a[j];
}

Check it. I'm not sure If this works you could improve it to

for(int i = 0; i < n; ++i)
    b[i] = a[(i - k)%n];//here can be (i +/- k) it depends which direction u would shift

Answer 2

If you only want to copy the array into another array and shift them

ex : input = 1, 2, 3, 4, 5; output = 3, 4, 5, 1, 2

The cumbersome solution is

//no template or unsafe void* since you are a beginner

int* copy_to(int *begin, int *end, int *result)
{
  while(begin != end){
    *result = *begin;
    ++result; ++begin;
  }

  return result;
}

int main()
{
  int input[] = {1, 2, 3, 4, 5};
  size_t const size = sizeof(input) / sizeof(int);
  size_t const begin = 2;
  int output[size] = {0}; //0, 0, 0, 0, 0

  int *result = copy_to(input + begin, input + size - begin, output); //3, 4, 5, 0, 0
  copy_to(input, input + begin, result); //3, 4, 5, 1, 2

  return 0;
}

How could the stl algorithms set help us?

read_data remain as the same one you provided

#include <algorithm> //std::minmax_element, std::rotate_copy
#include <iostream>
#include <iterator> //for std::begin()
#include <numeric> //for std::accumulate()
#include <string>
#include <vector>

int main(int argc, char *argv[]) //don't use _tmain, they are unportable
{

const int INPUT_CAPACITY = 100;
double user_input[INPUT_CAPACITY];
int input_size = 0;
double average = 0;

cout << "Enter numbers.  Input negative to quit.:\n";

read_data(user_input, INPUT_CAPACITY, input_size);

auto const min_max = std::minmax_element (user_input, user_input + input_size); //only valid for c++11

std::cout << "The maximum value entered was " << min_max.second << "\n";
std::cout << "The lowest value entered was " << min_max.first << "\n";

double sum_output = std::accumulate(user_input, user_input + input_size, 0);
cout << "The sum of the value's entered is " << sum_output << "\n";

//I don't know the meaning of you count_value, why don't just output input_size?
double count_output = count_value(user_input, input_size);
cout << "You entered " << count_output << " numbers." << "\n";

cout << "The average of your numbers is  " << sum_output / count_output << "\n";

int shift;
std::cout<<"How many positions do you want to shift?"<<std::endl;
std::cin>>shift;
std::vector<int> shift_array(input_size);
std::rotate_copy(user_input, user_input + shift, user_input + input_size, std::begin(shift_array));


//don't know what are they for?
std::string str;

std::getline(std::cin,str);
std::getline(std::cin,str);

return 0;
}

if your compiler do not support c++11 features yet

std::minmax_element could replace by std::min_element and std::max_element std::begin() can replace by shift_array.begin()

I don't know what is the teaching style of your class, in my humble opinion, beginners should start with those higher level components provided by c++ like vector, string, algorithms and so on.I suppose your teachers are teaching you that way and you are allowed to use the algorithms and containers come with c++(Let us beg that your class are not teaching you "c with classes" and say something like "OOP is the best thing in the world").

ps : You could use vector to replace the raw array if you like