Question

I am writing code that compares 2 bytes which represent integers. I want to see if byte R is with +-10 of G. The problem I am having with the code is with the comparison in the if-statment near the end. The bytes never come out as being out of range, even when they should. I am sure the problem comes from how I am adding/subtracting the error_range, but I don’t know any other way to do it.

I first considered converting the bytes into integers but I cannot find any help with that online. If that would work better than what I am doing here, please tell me how to do it.

Any help is appreciated!

const char ERROR_RANGE = 0x1010; //warning: overflow in implicit constant conversion
char R, G; /2 separate bytes
char buffer; //enough space for 1 byte

image = fopen(fileName,"r"); //open file

fread(&buffer, 1, 1, image); //read 1 byte  
memcpy (&R,&buffer,1); //store it as R

fread(&buffer, 1, 1, image); //read 1 byte   
memcpy (&G,&buffer,1); //store it as G

fclose(image);

if((R >= (G + ERROR_RANGE)) && (R <= (G - ERROR_RANGE)))
{
    printf("Outside of range!\n");
}

Thanks.

Answer 1

Your problem is because your test says:

if (R is greater than or equal to G + ERROR) AND (R is less than or equal to G – ERROR)

it can’t be both.

Replace the && with || in the first instance.

A better test would be:

if (the difference of R and G is greater than ERROR)

which translates to:

if (abs(R - G) > ERROR_RANGE)
{
    printf("Error");
}