Implementing minimum heap without STL and classess in C++

Question

I have to read all the data(integers) from file into the array and then iterate the array to make minimum heap and adding them after the last element of the current heap. After reading into array I have to call SiftUp() on each element which means to move the int into the correct position in the array. Also, I have to count the integers as I read them and set the global heapSize to that. At the end of all the inputs I am trying to print out the first five elements of the min heap array. output is wrong. My code is not making any minimum heap and thats why output is random. What is wrong with the logic?

input file has 97 integers:

347
765
654
44
15
567
098 
//and so on

output:

Please enter the name of the file to open :data.txt
 at index 1 :284
 at index 2 :870
 at index 3 :319
 at index 4 :47
 at index 5 :312
 at index 1 :284    // i dont know why it started again
 at index 2 :870
 at index 3 :319
 at index 4 :47
 at index 5 :312     //stops here

my program:

using namespace std;

int heapSize;
void SiftUp(int arr[], int heapSize);
const int arr_Size=100;
int heapArr[arr_Size];
void minHeap(int heapArr[]);

int main()
{
    int integers;
    string fileName;
    ifstream infile;
    cout << "Please enter the name of the file to open :";
    cin >> fileName;
    infile.open(fileName.c_str());
    if(!infile)
    {
        cerr << "An eror occurred while openieng the file.";
        exit(1);
    }
    while(!infile.eof())
    {

        for (int i=0; i<arr_Size; i++){
            infile >> integers;
            heapArr[i]=integers;
            heapSize=i;
    }
}
infile.close();
minHeap(heapArr);
for (int count =1 ; count <=5 ; count ++)
{
    cout << " Min at index " << count  <<" :"<< heapArr[count] << endl;
}
return 0;
}

void SiftUp(int arr[], int heapSize)
{
    int p;
    if (heapSize==1) return;
    else p = heapSize/2;
    if (arr[p] > arr[heapSize]) return;
    else swap (arr[heapSize],arr[p]);
    SiftUp(arr, p);
    }

void minHeap(int arr[])
{
    for (int i=0; i <arr_Size ; i++){ 
        SiftUp(arr, heapSize);
    }
}

Stack Overflow isn't a free debugging service, and you should show your attempts at debugging the code with a debugger or other simpler methods such as debug print statements. You can also test each part of the code separately to figure out exactly which part of the code is causing the problem, and make a [mcve]. This won't be the only time you end up with a bug in your code, and learning to debug your programs will help you much more than having someone find the bug for you. Debugging your own code is an important skill in programming. See http://idownvotedbecau.se/nodebugging/. — BessieTheCookie, Aug 07 '18 at 03:46
See [why `eof()` in a loop condition is wrong](https://stackoverflow.com/q/5605125/9254539). — BessieTheCookie, Aug 07 '18 at 03:47

score 1 · Answer 1 · answered Aug 07 '18 at 05:41

using namespace std;

int heapSize;
const int arr_Size=100;
int heapArr[arr_Size];
int main()
{
 int integers;
 string fileName;
 ifstream infile;
 cout << "Please enter the name of the file to open :";
 cin >> fileName;
 infile.open(fileName.c_str());
 if(!infile)
 {
     cerr << "An eror occurred while openieng the file.";
     exit(1);
 }
 while(!infile.eof())
 {

     for (int i=0; i<arr_Size; i++){
         infile >> integers;
         heapArr[i]=integers;
         heapSize=i;
 }

 infile.close();
 build_minheap(heapArr,heapSize);
 for (int count =1 ; count <=5 ; count ++)
 {
     cout << " Min at index " << count  <<" :"<< heapArr[count] << endl;
 }
 return 0;
}

void min_heapify(int *a,int i,int n)
{
   int j, temp;
   temp = a[i];
   j = 2 * i;
   while (j <= n)
   {
       if (j < n && a[j+1] < a[j])
           j = j + 1;
       if (temp < a[j])
           break;
       else if (temp >= a[j])
       {
           a[j/2] = a[j];
           j = 2 * j;
       }
   }
  a[j/2] = temp;
  return;
 }
 void build_minheap(int *a, int n)
 {
    int i;
    for(i = n/2; i >= 1; i--)
    {
        min_heapify(a,i,n);
     }
 }

muzzi · Accepted Answer · 2018-08-16T07:29:03.763

Why are you using arrays to pass as parameters that are already globally defined. I have tried to fix up your code. Have look and do it as it is. Hope, it will work.

 int main()
{
    int integer;
    string fileName;
    ifstream infile;
    cout << "Please enter the name of the file to open :";
    cin >> fileName;                                                  // asks user to     input filename
    infile.open(fileName.c_str());                                    // opens file
    if(!infile)
    {
    cerr << "An eror occurred while openieng the file.";
    exit(1);
    }
    int i;
    for (i=1; i<arr_Size; i++){
    infile >> integer;
    if(infile.fail())break;
    heapArr[i]=integer;
    SiftUp(i);
    }
    infile.close();
    heapSize=i;
    for (int count =1 ; count <=5 ; count ++)
    {
    cout << count  <<" :"<< heapArr[count] << endl;
    }

    return 0;
}

void SiftUp(int heapSize){
int p;
if (heapSize==1) return;
p = heapSize/2;
if (heapArr[p] < heapArr[heapSize]) return;
swap (heapArr[heapSize],heapArr[p]);
SiftUp(p);
}

you do not need to declare and write those parameters again. Because you have already Globally declared them. — muzzi, Aug 16 '18 at 07:27
Just edit your code according to you requirement. Try to learn how to debug your own program. — muzzi, Aug 16 '18 at 07:30

Implementing minimum heap without STL and classess in C++

2 Answers2