Strings in C

In C, strings are a 1-d array of characters that has a null terminator. All of the string functions provided in the string.h library work on the assumption that there is a null terminator as the last character in the string. The string "Brenda" has 6 characters and the null terminator so the array must be declared to be at least size 7, "computer science" has 16 characters (the space is a character) and the null terminator so the array must declared to be of at least size 17.
As with arrays, in order to use a string, you need some tools. You must be able to declare strings, input them, output them, compare them, copy one string to another one (assignment concept), etc.
Languages provide the most common tools needed as part of the language.

Declaration

    char  name[20]; /* Name can have as many as 19 characters and the 
                       null terminator */
    char social_security[12]; /* 123-45-6789 and the null terminator */

Declaration and Initialization - Initialization is NOT assignment.

   char name[20] = "John";
   char doggie[5] = {'S', 'p', 'o', 't', '\0'};

Output
```
   char name[10] = "Thomas";

   printf("\nYour name is %s", name);
      
   puts("\nYour name is ");
   puts(name);
```
Both the printf() and the puts() output whatever is stored in name beginning with the first location and outputting one character at a time until a null terminator is found. The null terminator is automatically included in the literal strings "\nYour name is %s" used by printf() and "\nYour name is " used by puts.
Input
- scanf();
```
  
    char name[10];

    scanf("%s", name);
```
  scanf() gets all the characters found in the input stream up to the first white space character and puts those characters in the string represented by name and places the null terminator in the storage location following the last character. It does NOT check to see if the string is actually large enough to hold all the characters it places in the string. There is no error checking.
- gets();
```
    char name[10];

    gets(name);
```
  gets() gets all the characters found in the input stream up to the carriage return and puts those characters in the string represented by name. It also places the null terminator in the string following the last character. Again, there is no error checking to make sure the string is actually large enough to hold all the characters placed in the string.
Comparison
```
    
    int int_value;
    char string1[10] = "first", string2[10] = "second";

    int_value = strcmp(string1, string2);
 
```
C's string comparison functions returns 0 if the strings are the same, a value less than 0 if the first string1 is alphabetically before string2 and a value greater than 0 if string2 is alphabetically before string1. In this example, the value in int_value is less than 0.
Copy
```
      strcpy(string1, string2);
```
This procedure copies the value of string2 into string1. It is up to the programmer to make sure that string1 is large enough to hold string2.
Concatenation
```
      strcat(string1, string2);
```
The value in string2 is "added" to the value in string1. It is the responsibility of the programmer to make sure that string1 is large enough to hold the combined string. Example: Assume string1 is "hello" and that string2 is "goodbye". The new value of string1 after concatenation is "hellogoodbye".
Finding the length of a string
```
    int_value = strlen(string);
```
C provides the strlen() function which returns an integer representing the number of characters in the string. The null terminator is not counted. For example: "John" is length 4, "Smith" is length 5, "Tom Smith" is length 9.

Example - swapping strings - NOTE: I assume that MAX is used by all the strings. This may NOT be a reasonable assumption which makes the declaration and use of temp a weak design but this is still the most widely used method of swapping 2 strings.

   void swap_strings(char string1[], char string2[])
   {
     char temp[MAX];

     strcpy(temp, string1)
     strcpy(string1, string2)
     strcpy(string2, temp)
   }