Homework help Array Arguments

I have an assignment to write a program that calculates how many of each character an imput contains and list the characters according to frequency greater to lesser. I thought I might have figured it out by modifying a piece of code from the textbook decribing array arguments, but when I attempted to run the program it aborted. Would someone please tell me what I need to do differently?

Code:

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#include <stdio.h>
#include <stdlib.h>
# define N 52

int find_largest(int a[], int n);
int find_largest(int a[], int n)
{
      int i, max;

      max = a[1];
      for (i = 1; i < n; i++)
          if (a[i] > max)
          max = a[i];
      return max;
 }
main()
{
      int a[N];
      int count = 0;
      int i = 0;
      int largest;
      int *b;
      float percent;
      char ch;

    for (i = 0; i < 53; i++)
          a[i] = 0;


      printf ("Enter a line of text: ");
      ch = getchar();
      while (ch != '\n')
      {
      count++;
      if (ch == ' ')
        a[0]++;
        if (ch >= 'A' && ch <= 'Z')
        {
          i = ch;
            a[i - 64]++;
        }
          if (ch >= 'a' && ch <= 'z')
          a[ch - 70]++;
      ch = getchar();
      }
      printf ("\n\nFREQUENCY TABLE\n---------------\nChar Count %% of Total \n");
      printf ("---- ----- ---------- \nALL    %d    100.00%%\n", count);

      largest = find_largest(b, N);

      for (i = 0; i < 53; i++)
      {
        if (a[i] != 0)
        {
          if (i == 0)

              ch = ' ';
            else if (i >= 1 && i <= 26)
              ch = i + 64;
              else
              ch = i + 70;
          percent = (float)(a[i]) / (float)(count) * 100;
          printf ("\"%c\"    %d    %.2f%%\n", ch, b, percent);
          }
      }


      system("pause");
      return 0;
}

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Code:

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    for (i = 0; i < 53; i++)
          a[i] = 0;

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array overrun

I have some other problem than that... It runs fine when I take out

Code:

---

int find_largest(int a[], int n);
int find_largest(int a[], int n)
{
    int i, max;

    max = a[1];
    for (i = 1; i < n; i++)
        if (a[i] > max)
        max = a[i];
    return max;
 }

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and

Code:

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      int largest;
      int *b;
      largest = find_largest(b, N);

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then change b to a[i]
It just doesn't list the output according to frequency.

Hi,
mistake is.

Code:

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int find_largest(int a[], int n)  \\ You Have Passed (b,N); To it , 'N' is rite But pointer 'b' doesn't have any address to Array. Why??????????
{
      int i, max;

      max = a[1];
      for (i = 1; i < n; i++)    \\ Why You Start The Array From 1 \\
          if (a[i] > max)
          max = a[i];
      return max;
 }

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ok