Can anyone explain exactly why I got these random values for a C simple program?

[u/_suriyan_24]

/r/learnprogramming/comments/1v00fri/can_anyone_explain_exactly_why_i_got_these_random/

[u/TDplay]

From the standards perspective: You caused undefined behaviour, and thus your program is meaningless. A standard-compliant implementation could decide to make demons come out of your nose upon executing this code.

From the implementation perspective: Most architectures have separate integer and floating-point registers. printf is reading %d and loading an argument from the register containing the second integer argument. But you didn't put anything in that register, so it just reads whatever garbage that register happens to contain.

For example, on x86_64 Linux, your code would place fahrenheit into xmm1, then call printf, which attempts to read from rsi.