Page 119 - Programming Microcontrollers in C

104 Chapter 2 Advanced C Topics

if(!isalnum(*w=tolower(getch())))
{
ungetch(*w);
break;
}
*w=‘\0’;
return word[0];
}
The first executable statement

while(isspace(c=tolower(getch())));
includes two standard C functions. The function isspace() has
its prototype in the header file ctype.h. This function returns a
TRUE if its argument is a space and FALSE otherwise. The second
function, tolower(), is also prototyped in ctype.h. It tests
the argument and returns a lower case letter if the argument is upper
case. Therefore, this operation will loop until it receives a nonspace
input, and the lower case version of the letter input will be stored in c.
If c is not an EOF, it is put into the next open location of the word
array and the pointer into this array is incremented. If the return is an
EOF, the second if statement will execute. The if statement

if(!isalpha(c))
{
*w=‘\0’;
return c;
}

tests to determine if the character from the input stream is a letter.
isalpha() returns a TRUE if its argument is a letter and a FALSE
otherwise. If the character taken from the input stream is an EOF,
isalpha() will return a FALSE and the statement following the
if will be executed. In this case, a zero character is written to the
word, and the EOF is returned to the calling function.
If the return is a letter, the following sequence will be executed:

for( ; —lim >0 ; w++)
if(!isalnum(*w=tolower(getch())))
{
ungetch(*w);