Question

this C code

unsigned long int a, b, x;
float c, d, y;

a = 6;
b = 2;
x = a/b;

c = 6.0;
d = 2.0;
y = c/d;

printf("\n x: %d \n y: %f \n",x,y);

works correctly and prints out

x: 3 
y: 3.000000

however, when I change the first line to this

unsigned long long int a, b, x;

I get this output:

x: 3 
y: 0.000000 

this really boggles me… I haven’t changed anything with c,d, and y – why am I getting this? I’m using gcc on linux

Answer 1

For the latter one use:

printf("\n x: %llu \n y: %f \n",x,y);

Use u for unsigned integrals (your output is only correct because you use small values). Use the ll modifier for long longs otherwise printf will use the wrong size for decoding the second parameter (x) for printf, so it uses bad address to fetch y.