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