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In this tutorial, you will learning writing a C program to check input is a digit or an alphabet by using if-else statement in c. For your better understanding of the program, we have explained some examples and algorithms.

Problem statement

The problem is we have to write a C program that takes a character as input and checks whether it is a digit or an alphabet. Please see the below example to understand what is our program is all about

Example

Enter a character: 5
Output: The input is a digit.

Enter a character: A
Output: The input is an alphabet.

Enter a character: #
Output: The input is neither a digit nor an alphabet.

As you can see on the above example for the input “5” output it printed The input is a digit. Similarly for the input “A” output is printed The input is an alphabet. And for the input # output is printed The input is neither a digit nor an alphabet.

Algorithm

1. Start the program.
2. Declare a variable input of type char to store the input character.
3. Print a message asking the user to enter a character.
4. Read the input character using scanf and store it in the input variable.
5. Use if-else statements to check the category of the input character:
   • If input is between ‘a’ and ‘z’ or between ‘A’ and ‘Z’, print “The input is an alphabet.”
   • Else if input is between ‘0’ and ‘9’, print “The input is a digit.”
   • Else, print “The input is neither a digit nor an alphabet.”
6. End the program.

Program to Check a Given Input is a Digit or Alphabet

#include <stdio.h>
int main() {
    char input;
    printf("Enter a character: ");
    scanf("%c", &input);
    if ((input >= 'a' && input <= 'z') || (input >= 'A' && input <= 'Z')) {
        printf("The input is an alphabet.\n");
    }
    else if (input >= '0' && input <= '9') {
        printf("The input is a digit.\n");
    }
    else {
        printf("The input is neither a digit nor an alphabet.\n");
    }
    return 0;
}

Output 1

Enter a character: 4
The input is a digit

Output 2

Enter a character: r
The input is an alphabet

Program Explanation

• The program starts by including the necessary header file stdio.h.
• The main() function is defined.
• Inside the main() function, a variable input of type char is declared to store the user’s input.
• The program prompts the user to enter a character by printing the message “Enter a character: “.
• The scanf() function is used to read a character from the user, and the input is stored in the input variable using the & operator.
• The program checks the category of the input character using if-else statements:
  • The first if statement checks if the input is between ‘a’ and ‘z’ (lowercase alphabet) or between ‘A’ and ‘Z’ (uppercase alphabet). If true, it prints “The input is an alphabet.”
  • The else if statement checks if the input is between ‘0’ and ‘9’ (digits). If true, it prints “The input is a digit.”
  • If none of the above conditions are satisfied, the else statement executes and prints “The input is neither a digit nor an alphabet.”
• The return 0 statement ends the program.

Conclusion

This C program allows the user to enter a character and determines whether it is a digit or an alphabet using if-else statements. It covers all possible cases and provides the appropriate output based on the input.