The isdigit c function in C is a standard library function that helps determine whether a given character is a numeric digit (0–9). It is part of the header file and is commonly used in applications that require input validation, numeric parsing, or text processing. This article explores the isdigit() function, including its syntax, usage, return values, and examples to illustrate its practical applications. Syntax and Declaration The isdigit() function is declared in the header file as follows: c Copy Edit #include int isdigit(int ch); Parameters ch: The character to be checked. It is passed as an int but is usually a char type cast to int. Return Value Returns a nonzero (true) value if ch is a digit (0–9). Returns 0 (false) if ch is not a digit. Usage and Examples Example 1: Basic Usage of isdigit() c Copy Edit #include #include int main() { char ch = '5'; if (isdigit(ch)) { printf("'%c' is a digit.\n", ch); } else { printf("'%c' is not a digit.\n", ch);fisdigit } return 0; } Output: csharp Copy Edit '5' is a digit. Example 2: Checking Multiple Characters c Copy Edit #include #include int main() { char str[] = "Hello123"; int i = 0; while (str) { if (isdigit(str)) { printf("'%c' is a digit.\n", str); } i++; } return 0; } Output: csharp Copy Edit '1' is a digit. '2' is a digit. '3' is a digit. Practical Applications 1. Input Validation When taking user input, isdigit() helps ensure that only numeric values are accepted. c Copy Edit #include #include void validateInput(char ch) { if (isdigit(ch)) { printf("Valid input: %c is a digit.\n", ch); } else { printf("Invalid input: %c is not a digit.\n", ch); } } int main() { char input; printf("Enter a character: "); scanf(" %c", &input); validateInput(input); return 0; } 2. Extracting Digits from a String In scenarios where a string contains a mix of characters and numbers, isdigit() can help extract numeric values. c Copy Edit #include #include void extractDigits(char str[]) { printf("Digits in the string: "); for (int i = 0; str != '\0'; i++) { if (isdigit(str)) { printf("%c", str); } } printf("\n"); } int main() { char str[] = "C Programming 101!"; extractDigits(str); return 0; } Output: csharp Copy Edit Digits in the string: 101