The printf function also recognizes a $8$ p format specifier, which expects a value of type "pointer". However, unlike the $8$ s format, $8$ p tells printf to simply print the address as a hexadecimal number. $($This can sometimes be useful in debugging, for getting a general idea where something is pointing.$)$ Create the programs hello$3[$abc$].$c by editing hello$2[$abc$].$c and only changing the $8s$ format specifier to $8$ p in each one. Compile and run each program. What do you observe about the addresses? How do they differ?

Now create hello$4[$abc$].$c by copying$/$editing hello$2[$abc$].$c to insert the following lines after the call to printf in each:

whomtogreet $[3]={?}^{\text{'}}k\text{'}$;

whomtogreet $[4]=073$;

printf$("$Hello$,\%$s$!$

$",$ whomtogreet$)$;

Compile and run hello$4$a$.$c$,$ then hello$4$b$.$c$.$ Do you see what is happening? Note that hex $73($decimal $115)$ is the ASCII code for $\text{'}$s$\text{'}.$ You can change the individual elements of a character string stored in a declared array. Also, char variables store $8-$bit values; the interpretation of those values is up to the software$-$in this case, printf.

Now compile and run hello$4$c$.$c$.$ What is different? To find out where the problem is$,$ recompile with debugging enabled by giving the $-g$ flag to the compiler: This tells the compiler to include information the debugger can use. Now run the program under the debugger: gdb $./$a$.$out and give the command run at the $($gab$)$ prompt. The debugger will show you which line of the program caused the "segmentation fault". There are two takeaways to note here:

First: We saw $($above$)$ that the name of an array variable can be interpreted as a value of type char $*.$ In a similar way, a variable of type char $*($as whomtogreet is declared in this program$)$ can be used like the name of an array, with brackets to denote an offset. So whomtogreet $[3]$ denotes a value of type char.

Second: string constants $($literals$)$ like "world" are stored in a read$-$only area of memory. When our hello$4$c program tries to change the contents of the string, it crashes. Bottom line: string literals cannot be modified at runtime.

End your script session by typing exit or control$-$D$.$ Verify that the script file exists in your current directory using the $15$ command, which, without any arguments, lists the files in the current directory. The output of $15$ should show your hello$*.$c files, plus one a$.$out file, plus your script file. $($Note: You should see a message of the form "Script done" when you end the script session. If you don't see it$,$ wait a few seconds and type ${?}^{{?}^{{?}^{?}}}D$ a few more times. NEVER look at your script output file if the script$\_$program might still be running$-$it will effectively disable your VM and you will probably have to get help from CS IT$.)$

Delete the a$.$out file with the $rm("$remove$")$ command:

Go back to the parent directory of cs$270$labo $($that is most likely your home directory$).$ You should be able to get there by doing popd or cd $....($Also$,$ cd with no arguments will always take you to your home directory.$)$