C isalnum() function
C isalnum(int ch)
The isalnum() function is used to check whether the argument ch is a character of class alpha or digit in the current locale. The function is defined in the ctype.h header file.
Syntax:
int isalnum(int argument);
isalnum() Parameters:
Name | Description | Required /Optional |
---|---|---|
ch | Argument ch represents a character. | Required |
isalnum() Return Value:
- The isalnum() function returns non-zero if ch is an alphanumeric character; otherwiset returns 0.
Example-1: isalnum() function return value
#include <stdio.h>
#include <ctype.h>
int main()
{
char ch;
int result;
ch = '8';
result = isalnum(ch);
printf("Return value is %d When %c is passed as an argemdent.", result, ch);
ch = '$';
result = isalnum(ch);
printf("\nReturn value is %d When %c is passed as an argemdent.", result, ch);
ch = '+';
result = isalnum(ch);
printf("\nReturn value is %d When %c is passed as an argemdent.", result, ch);
ch = 'A';
result = isalnum(ch);
printf("\nReturn value is %d When %c is passed as an argemdent.", result, ch);
ch = '-';
result = isalnum(ch);
printf("\nReturn value is %d When %c is passed as an argemdent.", result, ch);
return 0;
}
Output:
Return value is 4 When 8 is passed as an argemdent. Return value is 0 When $ is passed as an argemdent. Return value is 0 When + is passed as an argemdent. Return value is 1 When A is passed as an argemdent. Return value is 0 When - is passed as an argemdent.
Example #2: Check whether a character is an alphanumeric or not!
#include <stdio.h>
#include <ctype.h>
int main()
{
char ch;
printf("Input a character: ");
scanf("%c", &ch);
printf("Check the said number is alphanumeric characte or not!");
if (isalnum(ch) == 0)
printf("\n%c is not an alphanumeric character.", ch);
else
printf("\n%c is an alphanumeric character.", ch);
return 0;
}
Output:
Input a character: J Check the said number is alphanumeric characte or not! J is an alphanumeric character.
C Programming Code Editor:
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C Programming: Tips of the Day
Reading a string with scanf :
An array "decays" into a pointer to its first element, so scanf("%s", string) is equivalent to scanf("%s", &string[0]). On the other hand, scanf("%s", &string) passes a pointer-to-char[256], but it points to the same place.
Then scanf, when processing the tail of its argument list, will try to pull out a char *. That's the Right Thing when you've passed in string or &string[0], but when you've passed in &string you're depending on something that the language standard doesn't guarantee, namely that the pointers &string and &string[0] -- pointers to objects of different types and sizes that start at the same place -- are represented the same way.
Ref : https://bit.ly/3pdEk6f
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