Thread: Finding the problem creating bug during runtime

I have been asked to make an array program which includes merging, sorting, averaging inserting, deleting arrays etc....
While almost all the program has been made, i find few bugs giving false results during runtime ( no error though)... Though whole source code was copied from book, so it must be correct indeed.

The problem is while i enter even number of arrays, it says array is not sorted, even if its sorted and in inser sort, these value creates problem
2 4 6 8 10; no to be inserted =1...

Here it is part of that program

Code:

#include<stdio.h>
#include<conio.h>
void insertsorted(int *,int *,int);
void mergesort(int *,int,int *,int, int *);
int checksort(int *, int *);
main()
{
    int item,n,choice,l,b,k,i,m,p,checkcounter;
    char rerun;

    point1:
    printf("\n Enter your choice for array operations\n\n");

    printf("\n\t5. Insert in sorted array");

    printf("\n\t10. Merge two sorted array");
    printf("\n\t11. Exit");
    printf("\n\n Your selected choice is: ");
    scanf("%d",&choice);
    if((choice<1)||(choice>11))
    {
        printf("Wrong value entered; please try again");
        getch();
        system("cls");
        goto point1;
    }
    if(choice==11)
    {
        printf("\n Thanks for using the program\n Have a great day!!!");
        getch();
        exit(0);
    }
    printf("\nEnter element size: ");
    scanf("%d",&n);
    int A[n];
    printf("\nEnter %d elements of the array: \n",n);
    for(i=0;i<n;i++)
    scanf("%d",&A[i]);
    printf("\nThe elements of arrays are: ");
    for(i=0;i<n;i++)
    printf("%d\t",A[i]);
    if(choice==10)
    {
        printf("\nEnter element size of second array");
        scanf("%d",&m);
        p=m+n;
        int B[m],sorted[p];
        printf("\nEnter %d elements of the array: \n",m);
        for(i=0;i<m;i++)
        scanf("%d",&B[i]);
        printf("\nThe elements of arrays are: ");
        for(i=0;i<m;i++)
        printf("%d\t",B[i]);
        checkcounter=checksort(A,&n);
        if(checkcounter==-1)
        {
            printf("\n\n The element of this array are not sorted, please insert a sorted array");
            printf("\n Thanks for using the program\n Have a great day!!!");
            getch();
            exit(0);
        }
        checkcounter=checksort(B,&m);
        if(checkcounter==-1)
        {
            printf("\n\n The element of this array are not sorted, please insert a sorted array");
            printf("\n Thanks for using the program\n Have a great day!!!");
            getch();
            exit(0);
        }
        mergesort(A,n,B,m,sorted);
        printf("\nThe new array is:\n");
        for(i=0;i<p;i++)
        {
            printf("%d\t",sorted[i]);
        }
        getch();
    }
    switch (choice)
    {
        case 5:
        checkcounter=checksort(A,&n);
        if(checkcounter==-1)
        {
            printf("\n The element of this array are not sorted, please insert a sorted array");
            break;
        }
        printf("\nEnter number to be inserted in array");
        scanf("%d",&item);
        insertsorted(A,&n,item);
        printf("\nThe new array is:\n");
        for(i=0;i<n;i++)
        {
            printf("%d\t",A[i]);
        }
        break;
        case 10:
        break;
        default:
        printf("\n Wrong option selected; please try again");
        getch();
        system("cls");
        goto point1;        
    }
    getch();
    system("cls");
    printf("\n Do you want to re run the program??? (y to continue; any other key to exit): ");
    fflush(stdin);
    scanf("%c",&rerun);
    if(rerun=='y')
    {goto point1;}
    system("cls");
    printf("\n Thanks for using the program\n Have a great day!!!");
    getch();
}
void insertsorted(int *a, int *n, int item)
{
    int k;
    k=*n-1;
    while((item<a[k])&&(k>=0))
    {
        a[k+1]=a[k];
        a--;
    }
    a[k+1]=item;
    (*n)++;
}
void mergesort(int *a, int m, int *b, int n, int *c)
{
    int na, nb, nc;
    na=nb=nc=0;
    while((na<m) && (nb<n))
    {
      if(a[na]<b[nb])
      c[nc]=a[na++];
      else
      c[nc]=b[nb++];
      nc++;
      }
      if(na==m)
      {
      while(nb<n)
      c[nc++]=b[nb++];
      }
      else if (nb==n)
      {
           while(na<m)
           c[nc++]=a[na++];
           }
           }
int checksort(int *a, int *n)
{
    int i=0;
    
    while(i<*n)
    {
        if(a[i]>a[i+1])
        {
            return -1;
        }
        i++;
    }
    return 0;
}

checkcounter returns -1, on entering array with even numbers 2nd time.... Be it merge sorted array or re running program via y character when prompted...

Originally Posted by ashu123

Though whole source code was copied from book, so it must be correct indeed.

I wouldn't assume any code from a book is correct, especially from a book by Herbert Schildt. If this code is from one of his books, throw it out immediately (the book and the code). His writing is clear and sounds confident about the C language, but it's rubbish more often than not.

That said, I couldn't read the code past all of the non-standard code and poor style. Even if this is not from a Schildt book, I still recommend getting a better book.

Originally Posted by iMalc

No book worth its weight would use a goto where a loop is such a simple and obvious easy alternative. Nor would it pass n as a pointer to insertsorted or checksort. Nor would it have a buffer overrun inside checksort. Everything else you wrote indicates that you are writing this yourself. So, enough of this crap about the whole thing being from a book!

Turn your compiler warning levels up and pay attention to them.
The buffer overrun I mentioned is the most likely cause of the problem you know about.

Code is from book was referenced to function which is created; main is written by me and that is too obvious, cause no book will provide whole source code all the functioning in one program....

Originally Posted by christop

I wouldn't assume any code from a book is correct, especially from a book by Herbert Schildt. If this code is from one of his books, throw it out immediately (the book and the code). His writing is clear and sounds confident about the C language, but it's rubbish more often than not.

That said, I couldn't read the code past all of the non-standard code and poor style. Even if this is not from a Schildt book, I still recommend getting a better book.

I am using Data Structure using C by RS Salaria.... Dont know how good it is... But i would like to mention his book only provide source code of function.. Main is written by me cause we were asked to club all the function in a menu driven format....

Code:

void insertsorted(int *a, int *n, int item)
{
    int k;
    k=*n-1;
    while((item<a[k])&&(k>=0))
    {
        a[k+1]=a[k];
        a--;
    }
    a[k+1]=item;
    (*n)++;
}

If that function is copied from the book than I think you should stop reading it immediatetly because that function is just crap (it doesn't allocate space for the additional item, thus overwrites memory after the array and uses a very strange technique to go through the array)

Bye, Andreas

Originally Posted by AndiPersti

it doesn't allocate space for the additional item

Isnt (*n)++ for the same??
Besides, I have just pointed out the mistake in line 122 ( line 8 in insertsorted function), its actually k-- instead of a--. it was minor print mistake...
Now insertsort function works with the given set of values (2 4 6 8; inserted number =1)
Now problem comes with re running the program with same number of elements as earlier (example 4 in above) and taking two same even sized array in merge sort. Checksort returns -1 whenever its run second time (with even numbers)