12-bit Hamming Code

#include <stdio.h>
#include <math.h>
#include <string.h>
#include <stdlib.h>
//#include <conio.h>

int input[8], code[12];

void chtoi(int* arr, char* str, int len)
{
    int i;
    for(i = 0; i < len; i++)
    {
        if(str[i] == 48)
            arr[i] = 0;
        if(str[i] == 49)
            arr[i] = 1;
    }
}

void hamming(int* arr)
{
    int P1, P2, P3, P4;
    int i, j = 0;
    P1 = arr[0] ^ arr[1] ^ arr[3] ^ arr[4] ^ arr[6];
    P2 = arr[0] ^ arr[2] ^ arr[3] ^ arr[5] ^ arr[6];
    P3 = arr[1] ^ arr[2] ^ arr[3] ^ arr[7];
    P4 = arr[4] ^ arr[5] ^ arr[6] ^ arr[7];
    code[1-1] = P1;
    code[2-1] = P2;
    code[4-1] = P3;
    code[8-1] = P4;

    for(i = 0; i < 12; i++)
    {
        if(i != 0 && i != 1 && i != 3 && i != 7)
        {
            code[i] = arr[j];
            j++;
        }
    }
}

int main()
{
    int len, i;
    char chinput[8];
    printf("\nEnter the 8-bit binary number whose Hamming code you wish to find -: ");
    gets(chinput);

    if(strlen(chinput) != 8)
    {
        printf("\nThe number is not valid.");
        printf("\nHamming code generation failed.\n");
        //getch();
        exit(1);
    }
    chtoi(input, chinput, 8);
    hamming(input);
    printf("\nThe Hamming code is displayed as follows -: ");
    for(i = 0; i < 12; i++)
        printf("%d", code[i]);
    printf("\n");
    //getch();
    return 0;
}