Using namespace std ошибка

#include <iostream>
using namespace std;
int main(){
   cout << "hello world!";
}

#include <iostream>
#include <fstream>
using namespace std; 
void swap(int *element1, int *element2){
    int tmp = *element1;
    *element1 = *element2;
    *element2 = tmp;
}
void quicksort(int *inputfield, int n){
    cout << "{\ninputfield: ";
    for(int i = 0;i<n;i++){
        cout << inputfield[i] << " ";
    }
    cout << "\n";
    if(n>2){
        //getting the pivot:
        int pivot;
        {
            double pivotaverage = (inputfield[0] + inputfield[n/2] + inputfield[n-1])/3; // average of those pivots
            double a,b,c;
            a = abs(inputfield[0] - pivotaverage);
            b = abs(inputfield[n/2] - pivotaverage);
            c = abs(inputfield[n-1] - pivotaverage);
            if(a<=b && a<=c)pivot = 0; // getting the closest to average
            else if(b<=a && b<=c)pivot = n/2; //getting the closest to average
            else pivot = n-1; // getting the closest to average
            cout << "pivot index: " << pivot << "\n}\n";
            cout << "pivot value: " << inputfield[pivot];
        }
        int i = 0;
        for(int j = 0;j<n;j++){
            if(j == pivot)continue;
            if(i == pivot)i++;
            else if(inputfield[j] > inputfield[pivot])continue;
            else if(inputfield[j] <= inputfield[pivot]){
                //swap inputfield[i] with inputfield[j]
                int tmp = inputfield[i];
                inputfield[i] = inputfield[j];
                inputfield[j] = tmp;
            }
        }
        if(pivot < i){
            //swap pivot with with inputfield[i]
            int tmp = inputfield[i];
            inputfield[i] = inputfield[pivot];
            inputfield[pivot] = tmp;
            quicksort(inputfield, i+1);
            quicksort(inputfield + (i + 1) + 1, (n-((i+1)+1)));//give a pointer to element after the one that is scanned = (i+1) and skip the pointer = +1; then the length is n-that thing
        }
        else if(pivot > i){
            //swap pivot with inputfield[i+1]
            int tmp = inputfield[i+1];
            inputfield[i+1] = inputfield[pivot];
            inputfield[pivot] = tmp;
            quicksort(inputfield, i+1);
            quicksort(inputfield + (i + 1) + 1, (n-((i+1)+1)));//give a pointer to element after the one that is scanned = (i+1) and skip the pointer = +1; then the length is n-that thing
        }
    }
    else if(n == 2 && inputfield[0] > inputfield[1]){ // this is just to faster things up when it gets to the end
        int tmp = inputfield[1]; //Swap
        inputfield[1] = inputfield[0];
        inputfield[0] = tmp;
    }
    //if n = 1 or n = 0 there are no changes needed
}
int main(){
    int *field;
    int n;
    ifstream theFile("input.txt");
    string line;
    if(theFile){
        getline(theFile, line);
        for(int i = 0;line[i] != '\0';i++){
            if(line[i]<58 && line[i]>47){
                n = n*10+(line[i]-48);
            }
        }
        bool negative = false;
        field = new int[n];
        for(int i = 0;i<n;i++){field[i] = 0;}
        int g = 0;
        getline(theFile, line);
        for(int i = 0;line[i] != '\0';i++){
            if(line[i] == '-'){
                negative = true;
                cout << "hey";
            }
            else if(line[i] < 58 && line[i] > 47){
                field[g] = field[g]*10+(line[i]-48);
            }
            else{
                if(negative)field[g] = 0 - field[g];
                negative = false;
                g++;
            }
        }
        if(negative)field[g] = 0 - field[g];
    }
    else return 1;
    cout << n << '\n';
    for(int i = 0;i<n;i++){
        cout << field[i] << " ";
    }
    cout << "\n\n";
    quicksort(field, n);
    cout << "\n";
    for(int i = 0;i<n;i++){
        cout << field[i] << " ";
    }
    delete [] field;
} 

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#include <iostream>

using namespace std;

int main( void ) {

  std::cin.ignore();
  return 0;
}

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