Counting sort problem in c++ , compiler shows no output

Question

Counting Sort problem in c++

I tried to write a counting sort algorithm in c++. But this program is not working. I tried to debug, but can't find the problem. Compiler shows no output(code is attached in the below). Can anyone tell me, What's going wrong in this code?

How can I fix this problem?

#include <bits/stdc++.h>

using namespace std;

void printArray(int a[], int n){
    for(int i=0;i<n;i++){
        cout<<a[i]<<" ";
    }
    cout<<endl;
}

int main()
{
    int n;
    cin>>n;
    int a[n];
    for(int i=0;i<n;i++){
        cin>>a[i];
    }
    
    
    cout<<"Before Sort: ";
    printArray(a,n);
    
    
    //step-1: Find Maximum
    int max=INT_MIN;
    for(int i=0;i<n;i++){
        if(a[i]>max){
            max=a[i];
        }
    }
    //step-2: Initialization count+1 as 0
    
    int count[max+1];
    for(int i=0;i<=max;i++){
        count[i]=0;
    }
    
    
    //step-3 Frequency calculation
    
    for(int i=0;i<n;i++){
        count[a[i]]++;
    }
    
    
    //step-4 Cumlative sum
    
    for(int i=1;i<=max;i++){
        count[i]+=count[i-1];
    }
    
    
    //step-5: Final array --> Backword traversal of basic array
    
    int final[n];
    
    for(int i=n-1;i>=0;i++){
        count[a[i]]--;
        int k=count[a[i]];
        final[k]=a[i];
    }
    
    
    
    cout<<"After Sort: ";
    printArray(final,n);
    
    return 0;
}

Answer 1

I've changed all of your dynamically size arrays to vectors. I also changed your cumulative sum and backtracking loops to better match a counting sort.

#include <bits/stdc++.h>

using namespace std;

void printArray(vector<int> a, int n){
    for(int i=0;i<n;i++){
        cout<<a[i]<<" ";
    }
    cout<<endl;
}

int main()
{
    int n;
    cin>>n;
    vector<int>a(n);
    for(int i=0;i<n;i++){
        cin>>a[i];
    }
    
    
    cout<<"Before Sort: ";
    printArray(a,n);
    
    
    //step-1: Find Maximum
    int max=INT_MIN;
    for(int i=0;i<n;i++){
        if(a[i]>max){
            max=a[i];
        }
    }
    //step-2: Initialization count+1 as 0
    
    vector<int> count(max+1,0);
    
    
    //step-3 Frequency calculation
    
    for(int i=0;i<n;i++){
        count[a[i]]++;
    }
    
    
    //step-4 Cumlative sum- NOT NEEDED
    
    //for(int i=1;i<=max;i++){
    //    count[i]+=count[i-1];
    //}
    
    
    //step-5: Final array --> Backword traversal of basic array
    
    vector<int> final(n);
    int index=0;
    //iterate through frequency list
    for(int i=0;i<max;i++){
        //add any elements to sorted list
        for(int j=0;j<count[i];j++){
             final[index]=i;
             index++;
         }
    }
    
    
    
    cout<<"After Sort: ";
    printArray(final,n);
    
    return 0;
}