Today we are going to provide you with a detailed overview of the isalpha function in the C programming
language.
For the reader's convenience, this tutorial is split up into three following parts:
Return: non-zero value if int c is an alphabetic value. Otherwise, 0.
Parameter list: (int
c) - the character that is checked to determine the return value.
Header file:<ctype.h>.
1. So, what is the isalpha function in C?
This function in C language checks if the passed char
value is in the alphabet (uppercase or lowercase) or not, and returns appropriate value of type int
indicating the result.
If the argument is not in an alphabet , function isalpha returns 0.
If the argument is in an alphabet, a non-zero value is
returned.
The isalpha function is defined in the standard C library - <ctype.h>. For this function to be
usable, we have to include this library in our program (e.g. #include
<ctype.h>).
Example 1: the isalpha function in C.
#include<ctype.h>
#include<stdio.h>
intmain(void)
{
printf("%d\n",isalpha('a' - 1));
printf("%d\n",isalpha('a'));
return(0);
}
Possible output:
0 1
2. How to rewrite the isalpha function in
C?
Consider the code snippet below for a second:
Example 2: rewritten isalpha function in C.
intour_isalpha(intc)
{
if( ( c>=65&&c<=90) || ( c>=97&&c<=122 ) )
return(1);
return(0);
}
The our_isalpha function above takes one parameter. This
parameter gets implicitly typecasted to an according numerical value.
Then it is checked if the received value of c is in the range
of
[65, 90] or in the range of [97,122] (On line 3). If this condition is true, it means that the
value is in
the uppercase or lowercase alphabet and 1 is returned. Otherwise 0 is returned, indicating that the
value c is not in any alphabet, neither in lowercase nor in
uppercase.
Example 3: Test of the rewritten isalpha function in C.
#include<stdio.h>
intour_isalpha(intc)
{
if( ( c>=65&&c<=90) || ( c>=97&&c<=122 ) )
return(1);
return(0);
}
intmain(void)
{
printf("%d\n",our_isalpha('a' - 1));
printf("%d\n",our_isalpha('a'));
return(0);
}
Possible output:
0 1
Feel free to run the given test to see if we have successfully rewritten the isalpha function in the C
programming language.
Note: giving 'a' - 1 as an argument (on line 10) returns
0, because 'a' - 1 is equal to 64 and 64 is outside the alphabet ranges.
