So here's the code:
int create_mask(unsigned b, unsigned e)
{
unsigned int mask=1;
if(b<e || b<0 || e<0)
{
printf("Wrong values, starting bit can't be smaller than ending.\n");
printf("Both got to be >= 0.\n");
exit(EXIT_FAILURE);
}
while(b>0)
{
printf("%u\n", b);
mask<<=1;
if(b>e)
mask|=1;
b--;
}
return ~mask; /* negates mask for later purpose that is clearing corresponding bits */
}
Function creates mask for some bit operations, but should take two unsigned ints b and e, both non-negative. Question is how to prevent user input of negative numbers? When function is called with (-1,0) it start the loop, and shoult exit with error.
You could just input a string, check if it contains a
'-'
character, and yield an error if it does. Else you convert it to an unsigned integer and proceed on. (Reading as a string then converting withstrtoul()
is preferred over usingscanf()
anyway, especially while you aren't aware of all of the quirks ofscanf()
.)