What is RAM?

By definition Random Access Memory is the place in a computer where the operating system, application programs, and data in current use are kept so that they can be quickly reached by the computer's processor. RAM is much faster to read from and write to than the other kinds of storage in a computer, the hard disk, floppy disk, and CD-ROM.  However, all the data stored in RAM is only stored while the computer is running, after you shut it off all data is erased. 

First, let us remember that characters require 1 byte of storage in RAM or 8 bits.  On the other hand, storing integers (the data type int) require 2 CONTIGUOUS bytes (16 bits) of storage in RAM.  Now lets consider the following example:

                   C declaration:

                        int a, b = 'W', c= 1543;                      

We have declared the variables a, b, and c as integers (data type int), meaning that they require 2-bytes (16 bits) of storage each.  We are requesting a total of 6-bytes (48 bits; 16-bits per variable) be set aside in RAM at locations a, b, and c.

 Let us assume that locations 652, 653, 654, 657, 658, 662, 653 are available (i.e. 655, 656, 658-661 are being used).  In this case, variable a will be assigned to address 652 (and 653), variable b will be assigned to address 657(and 658) and variable c will be assigned to 662 (and 663), and initialized with the value 1,543.

The reason numbers are skipped is that integers require 2 contiguous bytes of memory. Because some of the addresses are not available, they are skipped and go on to the next available storage.  Locations 652 and 653 already have a value associated with them.  Even though we have not yet stored anything there, what was previously stored there is still there.

Contrary to other programming languages C and C++ do not clear the contents of an address when a variable is assigned to a particular address. Other programs, like Cobol, when allocating a variable to an address, get rid of whatever is stored at that particular address.  C and C++ keep whatever value is stored in that address until we actually set a value to the variable.

 Keep in mind that c programming language allows for additional integer data types. Such as:

unsigned integers.  This allows the storage of all values from 0 to 65,535 (2¹⁶ - 1), 16-bits(2-bytes)

longs. This allows the storage of all integers from (-2,147,483,648 to 2,147,483,647 (-2³¹ to 2³¹ -1), 32-bits(4-bytes)

unsigned longs.  This allows for the storage of all value from 0 to 4,294,967,296 (2³² -1), 32-bits(4-bytes)

 *Unsigned integers are stored exactly the same as integers except that we never have to worry about complimenting.  

   Let's not forget that integers are really stored on 32-bits.

One more time for reviewing sake, if we assume that an integer is stored in a particular location in RAM and we go and look at that address we will find 1 byte or 8 bits. The contents of that particular address are determined by whether if we have initialized the variable or not. If we did initialize it the contents will be whatever value we assigned to the variable; if, on the contrary, we did not initialize the variable we will get whatever value was stored at the location also called garbage.

Now let’s test your understanding with the following questions:

If we see the following statement unsigned int how is the computer going to evaluate the contents of that location?

Answer: The statement unsigned int will result in the computer evaluating all 8 bits to come out with the numeric value stored in the location.

Why do we get such strange output when printing out the contents of a declared ? And why does this happen?

Answer: Because by declaring a variable we are only requesting a location in RAM, we are not initializing it. Therefore, when printing out the contents of that variable, C++ will give us whatever character was stored there before. Remember that C and C++ do not clear the contents of the location in RAM when allocating an address.

How many contiguous bytes of storage would a long require?

            A- 2            B- 4                 C-6

Answer: B. A long would require 4 contiguous bytes (32-bits) or storage.

Can we print out an integer as a character?

Answer:  Yes, if a variable contains a certain value, we look at the rightmost 8-bits, determine the numeric value stored there, and then print out the corresponding ASCII character.

Here are a few References:

http://www.quepublishing.com/articles/article.asp?p=330332&rl=1

http://lib.daemon.am/Books/C/ch03/ch03.htm

Programming in C and C++