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C iscntrl() function

C iscntrl(int ch)

The iscntrl() function is used to check whether a character is a control character or not. The function is defined in the ctype.h header file.

Note: In computing and telecommunication, a control character or non-printing character (NPC) is a code point (a number) in a character set, that does not represent a written symbol. They are used as in-band signaling to cause effects other than the addition of a symbol to the text. All other characters are mainly printing, printable, or graphic characters, except perhaps for the "space" character.

Syntax:

int iscntrl(int argument);

iscntrl() Parameters:

Name Description Required /Optional
ch ch is a character of class cntrl in the current locale. Required

Return value from isupper()

  • The iscntrl() function returns non-zero if ch is a control character; otherwise, returns 0.

Example-1: Check control character


#include <stdio.h>
#include <ctype.h>

int main()
{
    char ch;
    ch = 'Q';
    printf("Check control character:");
    printf("\nIf %c is  cntrl character or not? %d", ch, iscntrl(ch));
    ch = ' ';
    printf("\nIf %c is  cntrl character or not? %d", ch, iscntrl(ch));
    ch = '\n';
    printf("\nIf %c is  cntrl character or not? %d", ch, iscntrl(ch));
    return 0;
}

Output:

Check control character:
If Q is  cntrl character or not? 0
If   is  cntrl character or not? 0
If
 is  cntrl character or not? 32

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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