CS520
Fall 2013
Lab 1
Due Wednesday, August 28

Write a program that takes a single command line argument and outputs the unsigned integer from the command line argument in little endian form in hex. Example:

```
./hex_int 0 
```
Should output
```
 00 00 00 00
```
```
./hex_int 1 
```
Should output
```
 01 00 00 00
```

Detailed instructions

Log on to one of the computers in the lab.
Open up a terminal
Make a directory entitled lab1
```
mkdir lab1
```
Change to the lab1 directory
```
cd lab1
```
In the lab1 folder, create a file called hex_int.c and write your program in this file.
To compile your file, in the lab1 directory type:
```
gcc -g -Wall -o hex_int hex_int.c
```
- -g indicates to compile the program with debugging information
- -o hex_int makes the compiler name the resulting binary hex_int instead of a.out
When you are done, submit your source file.
```
~cs520/bin/DoSubmission.py lab1 hex_int.c
```

Submitting

Please submit whatever you have at the end of lab, even if it is incomplete. You have the rest of today to finish this assignment.

Grading

75 points will be awarded for correctly outputting ordinary numbers.
5 additional points will be awarded for making sure there are the correct number of command line arguments.

10 additional points will be awarded for detecting invalid input

cmo66@zelinka:~/cs520/p1/lab1$ ./hex_int chris
chris is not a valid number

10 additional points will be awarded for detecting overflow

cmo66@zelinka:~/cs520/p1/lab1$ ./hex_int 9999999999999999999999999999999
9999999999999999999999999999999 is not a valid number (overflow)

Stuff you may find helpful

Printing an unsigned character

int x;
printf("%d ", x);

This is how you just write out an integer in decimal followed by a space. If you want to write out a character, you can basically do the same thing.

unsigned char x;
printf("%d ", x);

What if you want it printed nicely in hex?

unsigned char x;
printf("%x ", x);

What if you want the number to always take up 2 spaces?

unsigned char x;
printf("%02x ", x);

How do you turn a string into an integer?

There are a number of choices, I recommend strtoul. This function will allow you to detect all of the different error situations necessary for full credit.

Next Steps

The basics of this program are fairly straightforward, so it would not surprise me if some students finished early.

Writing to a file

I would recommend figuring out how to write numbers in little endian out to a file. Although there are a number of ways to write to a file, I found the function putc(int character, FILE* stream) to be useful for doing this.

Once you have attempted to write something to a file, you should check on what you wrote to make sure you like what it looks like. Usually you open up something you wrote in a text editor and make sure it is correct, but that won't work here, because if you did your job right, you won't have any text to look at. The easiest way to look at something in hex is to use od:

cmw@paris:~/cs520/p1/converter$ od -x output
0000000 d950 df21 3412
0000006

Reading from a file

To do program 1, you will also need to read something in binary from a text file.

CS520 Fall 2013 Lab 1 Due Wednesday, August 28