cbitmapbitmapdata

Printing bitmap in C


I am trying to create a bitmap of 100 1s and 0s.

Below is what i came out so far.. I having issue printing the bitmap or rather i do not know how to print the bitmap.

I want to display the bitmap that consist of all the 1 and 0 that i had set. for index 0 to 99

int main()
{

    unsigned int bit_position, setOrUnsetBit, ch;
    unsigned char bit_Map_array_index, shift_index;

    unsigned char bit_map[100] = { 0 };

    do
    {
        printf("Enter the Bit position (bit starts from 1 and Ends at 100) \n");
        scanf("%d", &bit_position);

        printf(" Do you want to set/unset the Bit (1 or 0) \n");
        scanf("%d", &setOrUnsetBit);


        bit_Map_array_index = (bit_position - 1) / 8;


        shift_index = (bit_position - 1) % 8;

        printf("The bit_position : %d shift Index : %d\n", bit_position, shift_index);

        if (setOrUnsetBit)
        {
            bit_map[bit_Map_array_index] |= 1 << shift_index; //set 1
        }
        else
        {
            bit_map[bit_Map_array_index] &= ~(1 << shift_index); //set 0
        }


        printf(" Do You want to Continue then Enter any Number"
            "and for Exit then enter 100\n");
        scanf("%d", &ch);



    } while (ch != 100);

    //I wan to print bitmap here after exiting

    system("pause");
    return 0;
}

I have very little experience in C programming... So correct me wherever i am wrong.

Thanks in advance.


Solution

  • You are working with bytes, not bits. You have 100 bytes, set each byte to 0 or 1. There is no need for shifting values:

    unsigned char bytes[100];
    for(int i = 0; i < sizeof(bytes); i++)
        bytes[i] = rand() % 2;
    
    for(int y = 0; y < 10; y++)
    {
        for(int x = 0; x < 10; x++)
        {
            int i = y * 10 + x;
            printf("%d ", bytes[i]);
        }
        printf("\n");
    }
    

    If you are working with bits, then you can use

    unsigned char data[13];
    

    Because 13 is 13 * 8 bits, or 104 bits. You only need 100 bits. How you set and get the bits, depends on the format you choose. A bitmap file, for example, is padded so each line is multiple of 4-bytes. In general you can set the values as:

    if(bytes[i])
        data[byteindex] |= (1 << shift);
    else
        data[byteindex] &= ~(1 << shift);
    

    To get the value back:

    int value = (data[byte] & shift) > 0;