Hex to decimal conversion

// Program accepts an 8 digit hexadecimal input and outputs
// the corresponding value in decimal

#include <stdio.h>

main()
{

    int decimal = 0; //integer for the final decimal number
    int bit; //integer representing numbers between 0-9 and letter a-f in hex number
    char hexnumber[100]; //a char array containing the input hex number

    int i=0,j=0;

    printf("Enter your hexadecimal number: ");
    scanf("%s",&hexnumber);

    //the integer i takes the length of the input array
    i =strlen(hexnumber);

    //while there is a next bit in the array
    while(i!=0)
    {
    bit = hexnumber[j];

    //if the bit is a digit do the following
    if(('0' <= bit && bit <= '9'))
    {
    decimal = decimal * 16;
    decimal = decimal + (bit - '0');
    }

    //if the bit is a letter do the following
    if(('a' <= bit && bit <= 'z'))
    {
    decimal = decimal * 16;
    decimal = decimal + (bit - '7');
    }

    i--;
    j++;

    }

    printf("The decimal representation of this number is : %d\n",decimal);

}

    //if the bit is a letter do the following
    if(('a' <= bit && bit <= 'z'))
    {
    decimal = decimal * 16;
    decimal = decimal + (bit - '7');
    }