A string exists only as a sequence of characters terminated by a special character known as the null character. The null character is actually an ASCII zero.  A numeric array is a data structure in which contains a fixed number of contiguous storage elements all of the same data type.  In conclusion a numeric array and string are the same except for two things:

Conclusion: A numeric array and a character array are the same except for these two things:                                                                                               

• Numeric arrays contain numeric values and not

character values.                                                                                                                   

• Numeric arrays don’t use a terminating null zero

(‘\0’).

Strings only take up 1-byte of storage per element.

When it comes to string we are only interested in keeping track of string offsets and how many elements are contained in a string.

We do not want to count them.

We really don't care much for strings since the only thing we do with strings is print them out.

Remember we cannot print out numeric values only symbols.

Things we need to know.

What Characters are?                                                     

How Characters are stored in RAM?                                      

Why we must convert strings?

How to manipulate characters.                                       

Where the strings begins?

We deal with strings by assigning a string of characters as follows:

mystring[0] = 'H';       or chararray[0] = 72;                                
mystring[1] = 'e';          chararray[1] = 101;
mystring[2] = 'l';          chararray[2] = 108;
mystring[3] = 'l';          chararray[3] = 108;
mystring[4] = 'o';          chararray[4] = 111;
mystring[5] = '\0';         chararray[5] = 0;

Remember strings require 1 additional byte at the end of the array; the NULL ('/0') character

"Converting Strings to Numbers" pg. 128

"When we enter numbers from the keyboard, we actually are entering numeric values which are stored as the data type char.  When we read them from the ASCII file, we are actually reading-in characters.  To store them in RAM as numeric values, so we can perform arithmetic operations on them, we must first convert them to their numeric equivalents."

First we need to determine if the character belongs to the set of digits.

As discussed in our slide show as well as class I am going to go over how to convert.

We know that it has to between '0' and '9' (inclusive) and if the character value is between 48 and 57,

we know that they are legal values.

The next lines deal with the converting process described above.

The loop was terminated because remember it stops once you reach the null character at the end of the string.  As well as in the code the declaration char nstring []="123"; automatically adds a NULL character at the end of the string.

Remember the basics; if a string consisted of the characters '54', the corresponding value would be equal to (5*10) + 4, or 54.  If  the string was '2633' the numeric equivalent would be (2 *1000) + (6 *100) + (3 *10) + 3 = 2633.

The following are references for additional information on strings:

1.  Do you have to use the maximum number of characters assigned?

No, you do not.  Please refer to the following demonstration.

2.  What are the two main differences between a string and a numeric array?

The two main differences between a string and a numeric array are:

a) numeric arrays contain numeric values

b) Strings use null to terminate value

3.  Null represents what decimal value?

a) 1

b) 2

c) 3

d) 0

(Answer: d) 0)

4.  How do we determine the address of an array?

a) base address

b) offset/script

c) base address plus offset/script

(Answer: c) base address plus offset/script)                                                                   

5. What does the function atoi do?

a) converts all character to integers

b) allows alphanumeric to integrate.

c) all of the above

d) converts a string to an integer

Answer: d (it converts a string to an integer)

6. Explain what the function ftoa does?

a) converts a string to an integer

b) converts a real number (float) to a string

c) it allow the float to be converted directly to the base address

d) none of the above

Answer: b (converts a real number (float) to a string)