isdigit() function in C

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The isdigit() function in C is used to determine if a character is a digit or not.

It checks whether a character falls within the range of '0' to '9'.

This function is part of the library, which provides functions for character classification.

Syntax:

int isdigit(int c);

Steps:

Include Header File: Include the header file at the beginning of your program to use the isdigit() function.

Call the Function: Pass a character or an integer representing a character as an argument to the isdigit() function.

Check Return Value: The function returns an integer:

If the character is a digit (0-9), it returns a non-zero value (typically 1).

If the character isn't a digit, the function returns 0.

Parameters:

c: It's an integer representing a character.

Return Value:

The isdigit() function returns an integer:

It returns a non-zero value (usually 1) if the character c is a digit.

It returns 0 if the character c is not a digit.

Examples:

Check if a Character is a Digit:

// Program to check if a character is a digit
#include<stdio.h>
#include<ctype.h>

int main() {
    char ch = '7';
    if (isdigit(ch)) {
        printf("%c is a digit\n", ch);
    } else {
        printf("%c is not a digit\n", ch);
    }
    return 0;
}

Output:

7 is a digit

Check if Characters in a String are Digits:

// program to check if characters in a string are digits
#include<stdio.h>
#include<ctype.h>

int main() {
    char str[] = "Hello123";
    for (int i = 0; str[i] != '\0'; ++i) {
        if (isdigit(str[i])) {
            printf("%c is a digit\n", str[i]);
        } else {
            printf("%c is not a digit\n", str[i]);
        }
    }
    return 0;
}

Output:

H is not a digit
e is not a digit
l is not a digit
l is not a digit
o is not a digit
1 is a digit
2 is a digit
3 is a digit

Count the Number of Digits in a String:

// program to count number of digits in a strings
#include<stdio.h> 
#include<ctype,h>

int main() {
    char str[] = "Hello123";
    int count = 0;
    for (int i = 0; str[i] != '\0'; ++i) {
        if (isdigit(str[i])) {
            count++;
        }
    }
    printf("Number of digits in the string: %d\n", count);
    return 0;
}

Output:

Number of digits in the string: 3

Extract Digits from a String:

program to extract digit from a string
#include<stdio.h> 
#include<ctype.h> 

int main() {
    char str[] = "Hello123";
    printf("Digits in the string: ");
    for (int i = 0; str[i] != '\0'; ++i) {
        if (isdigit(str[i])) {
            printf("%c ", str[i]);
        }
    }
    printf("\n");
    return 0;
}

Output: