Question

I have a homework. The question is:

Write a function that takes as parameter a single integer, int input, and returns an unsigned character
such that:
a- if input is negative or larger than 11,111,111 or contains a digit that is not 0 or 1; then the function will
print an error message (such as “invalid input”) and return 0,
b- otherwise; the function will assume that the base-10 value of input represents a bit sequence and return the magnitude-only bit model correspondent of this sequence.

For Example: If input is 1011, return value is 11 and If input is 1110, return value is 14

This is my work for a, and I am stuck on b. How can I get bit sequence for given integer input?

int main()
{
    int input = 0;

printf("Please type an integer number less than 11,111,111.\n");
scanf("%d",&input);

if(input < 0 || input > 11111111)
{
    printf("Invalid Input\n");
    system("PAUSE");
    return 0;
}


for (int i = 0; i < 8; i++)
{
    int writtenInput = input;
    int single_digit = writtenInput%10;

    if(single_digit == 0 || single_digit == 1)
    {
        writtenInput /= 10;
    }
    else
    {
        printf("Your digit contains a number that does not 0 or 1. it is invalid input\n");
    system("PAUSE");
    return 0;
    }
}

printf("Written integer is %d\n",input);

system("PAUSE");
return 0;
}

Answer 1

The bit that you are missing is the base conversion. To interpret a number in base B, what you need to do is multiply digit N times B^N (assuming that you start counting digits from the least significative). For example, in base 16, A108 = (10)*16^3 + 1*16^2 + 0*16^1 + 8*16^0. Where in your base is 2 (binary).

Alternatively, you can avoid the exponentiation if you rewrite the expression as:

hex A008 = ((((10*16) + 1)*16 +0)*16 + 8

Which would be simpler if your input was stated in terms of an array of possibly unknown length as it is easily convertible into a loop of only additions and multiplications.

In the particular case of binary, you can use another direct solution, for each digit that is non-zero, set the corresponding bit in an integer type large enough (in your case, unsigned char suffices), and the value of the variable at the end of the loop will be the result of the conversion.