Dewey Decimal always begins with a number: 

In both Dewey and LC, after the subject classification number, there is always a second line or element in the call number, beginning with a letter:  C368s, B64, etc.  This is generally refered to as a Cutter number (after the person who developed the system), and simply serves as a means of alphabetizing either the author or, if the work is about a person, the subject's name.

Dewey Decimal:  Call numbers are arranged first numerically, and then, within a specific number, alphabetically.  Notice that decimals count!

Within a Dewey number, the second line is shelved alphabetically, and then numerically.  Even though there's not a decimal next to the Cutter number, it is implied in the order in which numbers are arranged on the shelf:

Library of Congress always begins with letters: 

In both Dewey and LC, after the subject classification number, there is always a second line or element in the call number, beginning with a letter:  C368s, B64, etc.  This is generally refered to as a Cutter number (after the person who developed the system), and simply serves as a means of alphabetizing either the author or, if the work is about a person, the subject's name.

Library of Congress:  Call numbers are arranged first alphabetically, and then by the numbers that follow the letters.  On the first line, remember the rule, nothing comes before something:

After the initial letter(s), LC numbers are arranged by the value of the entire number:

After the first two lines, call numbers are arranged first alphabetically, and then according to the decimal:

SuDoc always begins with letters, but contains a colon:  

SuDoc:  Call numbers are arranged first alphabetically, with letters coming before numbers, and then numerically.  The only real tricks are to ignore "Senate Hearing" or "Senate Print," and to remember that what looks suspiciously like a decimal point in a SuDoc number is actually only a divider (as are any punctuation, such as / or :):  treat as whole numbers any numbers that follow punctuation:

Where are the call numbers found in the Library?

• Dewey Decimal books are on various floors. Check the Library Map to see where the specific number is.
• Library of Congress books are currently located on two floors:
  • A-BY is on Level F
  • C-HD is on Level D
  • HE-Z is on Level C, behind the Atrium, on the far side of the Reference Collection.
• SuDoc is primarily on Level A.