C on Institute of Ineptitude

Condition Evaluation Utility

Sat, 06 Dec 2025 21:41:18 -0700

After you run a command in UNIX shell (bourne, bash, etc), $? has the exit code (return value) of the prior run command:

 $? Expands to the exit status of the most recent pipeline.

Shell scripting is a bit weird in that the return value of a program is evaluated as true if it’s 0 and false if it’s non-zero.

This is useful as by convention unix commands return 0 on success or any other integer code to map to specific error conditions.

ASCII case bit twiddling

Tue, 10 Dec 2024 21:49:28 -0700

If you pay a special sort of attention, you may notice that the upper-case and lower-case alphabet characters on the ASCII table are always exactly offset from each other by 32.

For example, upper-case A is 65, while the lowercase a is 97

As such the way the binary place value works out, you can manipulate the case of a character by setting or clearing the sixth bit… (2^5 = 32, we start counting bits and everything at 0, we’re programmers!)

Decimal 32 expressed as hexadecimal is 0x20 and expressed as binary is 00100000

Initialize your variables

Sat, 17 Aug 2024 15:51:13 -0700

There’s no shortage of material that explains variables in C should be initialized… but I’ve often found the explanation of why to be somewhat lacking.

Where do the initial values of a variable come from if you don’t explicitly initialize?

Guess the number...

Fri, 05 Apr 2024 00:00:00 +0000

A quick demonstration of how one can use a debugger to interactively inspect variables in a running program…