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C isalpha() function

C isalpha(int ch)

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

Note: Letter (alphabet) - A letter is a segmental symbol of a phonemic writing system. The inventory of all letters forms an alphabet. Letters broadly correspond to phonemes in the spoken form of the language, although there is rarely a consistent and exact correspondence between letters and phonemes.

Syntax:

int isalpha(int argument);

isupper() Parameters:

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

Return value from isalnum()

  • The isalpha() function returns non-zero if ch is an alphabetic character; otherwise returns 0.

Example: C isalpha() function


#include <stdio.h>
#include <ctype.h>
int main()
{
    char ch;
    ch = 'A';
    printf("\nIf %c is alphabet or not? %d",ch, isalpha(ch));
    ch = '5';
    printf("\nIf %c is alphabet or not? %d",ch, isalpha(ch));
    ch = '+';
    printf("\nIf %c is alphabet or not? %d",ch, isalpha(ch));
    return 0;
}

Output:

If A is alphabet or not? 1
If 5 is alphabet or not? 0
If + is alphabet or not? 0

Example: C Program to test whether a character input from user is Alphabet or not

#include <stdio.h>
#include <ctype.h>
int main()
{
    char ch;

    printf("Input a character: ");
    scanf("%c", &ch);

    if (isalpha(ch) == 0)
         printf("%c is not an alphabet.", ch);
    else
         printf("%c is an alphabet.", ch);

    return 0;
}

Output:

Input a character: S
S is an alphabet.
------------------------ Input a character: 9 9 is not an alphabet.

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What's an object file in C?

An object file is the real output from the compilation phase. It's mostly machine code, but has info that allows a linker to see what symbols are in it as well as symbols it requires in order to work. (For reference, "symbols" are basically names of global objects, functions, etc.)

A linker takes all these object files and combines them to form one executable (assuming that it can, i.e.: that there aren't any duplicate or undefined symbols). A lot of compilers will do this for you (read: they run the linker on their own) if you don't tell them to "just compile" using command-line options. (-c is a common "just compile; don't link" option.)

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