i wrote a program that was supposed to run a function that makes a conversion of inter digits to binary

when i try to compile the program, the following errors come up:

int_to_bin.c:33: error: conflicting types for 'counv'
int_to_bin.c:28: error: previous implicit declaration of 'counv' was here
int_to_bin.c: In function 'counv':
int_to_bin.c:87: warning: return makes integer from pointer without a cast
int_to_bin.c:87: warning: function returns address of local variable

here is the code:
Code:
/********************************************************
 *							*
 * FILE: ch10_ex4.c					*
 * CREATED: 8/15/07					*
 * BY: bpf						*
 *							*
 *  this program will run a function that converts an	*
 *   integer to the binary code for each of the		*
 *   integer's digits					*
 *							*
 ********************************************************/

#include<stdio.h>
#include<string.h>

main()
{
  char line[100];
  char itgr[100]; /* the integer value of the input number */
  char conv(); /* function prototype */

  /* input number */
  (void)printf("enter an integer: ");
  (void)fgets(line, sizeof(line), stdin);
  (void)sscanf(line, "%s", &itgr);

  /* print new number */
  (void)printf("%c\n", counv(itgr));

  return(0);
}

char counv(char itgr[]) {

  int index; /* index into integer string */
  int length = strlen(itgr); /* length of string */
  char bin[100]; /* string for binary number */

  /* starting from the last digit, concatonize the binary equivalent to the binary string */
  for (index = length - 1; index < 0; index--) {

    switch(itgr[index]) {

    case '1':
      (void)strcat(bin, "0001");
      break;

    case '2':
      (void)strcat(bin, "0010");
      break;

    case '3':
      (void)strcat(bin, "0011");
      break;

    case '4':
      (void)strcat(bin, "0100");
      break;

    case '5':
      (void)strcat(bin, "0101");
      break;

    case '6':
      (void)strcat(bin, "0110");
      break;

    case '7':
      (void)strcat(bin, "0111");
      break;

    case '8':
      (void)strcat(bin, "1000");
      break;

    case '9':
      (void)strcat(bin, "1001");
      break;

    default:
      /* do nothing */
      break;

    } /* closes switch statement */
  } /* closes for loop */

  return(bin);
}