global variable problem - c

Question

i declare a global variable and use and modify its value in the function. Then i want to get the modified value of this global variable, it has some problem. Can anyone help me?
#include<stdio.h>
#include<string.h>
#include<conio.h>
#include<stdlib.h>
#define MAX 10
struct link
{
int freq;
char value[MAX];
struct link* right;
struct link* left;
};
typedef struct link node;
void sort(node *[], int);
node* create(char[], int);
void sright(node *[], int);
void Assign_Code(node*, int [], int);
void Delete_Tree(node *);
int test[720][720];
main()
{
node* ptr, * head;
int i, n, total = 0, u, c[256];
char str[MAX];
node* a[256];
int freq;
printf( "Huffman Algorithm\n");
printf("\nEnter the no. of letter to be coded:");
/*input the no. of letters*/
scanf("%d", &n);
for (i = 0; i < n; i++)
{
printf("Enter the letter & frequency:");
/*input the letter & frequency*/
scanf("%s %d", str, &freq);
a[i] = create(str, freq);
}
while (n > 1)
{
sort(a, n);
u = a[0]->freq + a[1]->freq;
strcpy(str,a[0]->value);
strcat(str,a[1]->value);
ptr = create(str, u);
ptr->right = a[1];
ptr->left = a[0];
a[0] = ptr;
sright(a, n);
n--;
}
Assign_Code(a[0], c, 0);
//getch();
printf("Code: ");
for (i = 1; i <= n; i++)
{
printf("%d", test[0][i]);
}
printf("\n");
Delete_Tree(a[0]);
}
node* create(char a[], int x)
{
node* ptr;
ptr = (node *) malloc(256*sizeof(node));
ptr->freq = x;
strcpy( ptr->value , a);
ptr->right = ptr->left = NULL;
return(ptr);
}
void sort(node* a[], int n)
{
int i, j;
node* temp;
for (i = 0; i < n - 1; i++)
for (j = i; j < n; j++)
if (a[i]->freq > a[j]->freq)
{
temp = a[i];
a[i] = a[j];
a[j] = temp;
}
}
void sright(node* a[], int n)
{
int i;
for (i = 1; i < n - 1; i++)
a[i] = a[i + 1];
}
void Assign_Code(node* tree, int c[], int n)
{
int i;
if ((tree->left == NULL) && (tree->right == NULL))
{
printf("%s code: ", tree->value);
test[0][0]=tree->value;
for (i = 0; i < n; i++)
{
test[0][i+1]=c[i];
printf("%d", c[i]);
}
printf("\n");
}
else
{
c[n] = 1;
n++;
Assign_Code(tree->left, c, n);
c[n - 1] = 0;
Assign_Code(tree->right, c, n);
}
}
void Delete_Tree(node * root)
{
if(root!=NULL)
{
Delete_Tree(root->left);
Delete_Tree(root->right);
free(root);
}
}

Answer 1

Let me highlight the problem:
while (n > 1)
{
...
n--;
}
...
for (i = 1; i <= n; i++)
{
printf("%d", test[0][i]);
}
By the time the second loop starts n is one, and the printf is executed only once, so that you print the value of test[0][1] and only that.
The value of test[0][1] is overwritten many times (as many as the number of leaf nodes in the tree) in Assign_Code:
void Assign_Code(node* tree, int c[], int n)
{
if ((tree->left == NULL) && (tree->right == NULL))
{
...
for (i = 0; i < n; i++)
{
test[0][i+1]=c[i];
}
}
...
}
Now, because of the way you are traversing the tree the last time test[0][1] is overwritten is for a Huffman code that has a '0' as first character.

Answer 2

As a side note:
node* create(char a[], int x)
{
node* ptr;
ptr = (node *) malloc(256*sizeof(node)); // <--- This is wrong
ptr->freq = x;
strcpy( ptr->value , a);
ptr->right = ptr->left = NULL;
return(ptr);
}
There is no reason to allocate 256 times the size of node to store one node. You are creating a node and storing it in an array of pointers to nodes. Allocate one node there, like this:
malloc (sizeof (node)); or malloc ((sizeof (*ptr));

Answer 3

you can store the n value to some temporary variables, after you get the
values.
Then use the temporary variable in your for loop condition.
scanf("%d", &n);
int temp = n ;
for (i = 1; i <= temp ; i++)
{
printf("%d", test[0][i]);
}