Learn to Program with C_ Learn to Program using the Popular C Programming Language ( PDFDrive )

Chapter 9 ■ Searching, Sorting, and Merging
9.4 Sort an Array of Strings
Consider the problem of sorting a list of names in alphabetical order. We have seen that, in C,
each name is stored in a character array. To store several names, we need a two-dimensional
character array. For example, consider the following list of names.
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
0 S a m l a l , R a w l E \0
1 W i l l i a m s , M a r k \0
2 D e l w i n , M a c \0
3 T a y l o r , V i c t o r \0
4 M o h a m e d , A b u \0
5 S i n g h , K R i s h n a \0
6 T a w a r i , T a u \0
7 A b d o o l , Z a i d \0
To store this list, we will require a declaration such as the following:
char list[8][15];
To cater for longer names, we can increase 15, and to cater for more names, we can increase 8.
The process of sorting list is essentially the same as sorting an array of integers. The major
difference is that whereas we use < to compare two numbers, we must use strcmp to compare two
names. In the function insertionSort shown earlier, the while condition changes from this:
while (k >= lo && key < list[k])
to the following, where key is now declared as char key[15]:
while (k >= lo && strcmp(key, list[k]) < 0)
Also, we must now use strcpy (since we can’t use = for strings) to assign a name to another
location. We will see the complete function in the next section.
9.4.1 Variable-Length Arrays
We will use this example to show how variable-length arrays (VLAs) may be used in C. This
feature is available only in C versions from C99 and later. The idea is that the size of an array may
be specified at runtime as opposed to compile time.
In the function below, note the declaration of list (char list[][max]) in the parameter
list. The size of the first dimension is left unspecified, as for one-dimensional arrays. The size
of the second dimension is specified using the parameter max; the value of max will be specified
when the function is called. This gives us a bit more flexibility since we can specify the size of the
second dimension at runtime.
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