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Here, in this tutorial, you will learn how to write a C program to count the digits of a given number using a while loop. We will see various examples, logic, algorithms, and program explanations for your better understanding of this program.

Required Knowledge

• C Programming Basics
• C Programming Operators
• C printf and Scanf
• While loop in C

Problem statement

You have to Write a C program that takes a number as input from the user. After taking the input you have to count the number of digits in the input number using a while loop. Program should provide a solution to find the count of digits in a number using a while loop in the C programming language.

For a better understanding, below we have an example that help you to understand what exactly we wanted to achieve in this program.

Example

Input:
Enter a number: 12345

Output:
The number of digits in 12345 is: 5

In the above example, you can see that the user has given input 12345. As the input number has 5 digits so output will print as 5.

Algorithm

1. Start the program.
2. Declare the variables: num to store the input number, count to store the count of digits, and temp as a temporary variable to hold the value of num.
3. Read the value of num from the user.
4. Initialize count to 0.
5. Assign the value of num to temp.
6. Enter the while loop with the condition temp != 0.
   • Divide temp by 10 to remove the last digit.
   • Increment count by 1.
7. Exit the while loop.
8. Print the count of digits as: “The number of digits in num is: count”.
9. End the program.

Logic used to solve this problem

• Declare a variable to hold the input number and another variable to store the count of digits.
• Prompt the user to enter a number.
• Read and store the entered number in the variable.
• Initialize the count variable to 0.
• Use a while loop that runs as long as the number is greater than 0.
• Inside the loop, increment the count variable by 1.
• Reduce the number by removing the last digit using the integer division (/) operator.
• Continue the loop until the number becomes 0.
• Print the count of digits.
• Finish the program.

Program to count the digits of a given number

#include <stdio.h>
int main() {
    int num, count = 0, temp;
    printf("Enter a number: ");
    scanf("%d", &num);
    temp = num;
    while (temp != 0) {
        temp /= 10;
        count++;
    }
    printf("The number of digits in %d is: %d\n", num, count);
    return 0;
}

Output

Enter a number: 10
The number of digits in 10 is: 2

Program Explanation

• The program takes input for the number whose digits are to be counted.
• It initializes a variable count to 0, which represents the count of digits.
• The program enters a while loop with the condition number > 0 to extract the digits of the given number.
• Inside the while loop, it calculates the remainder of the number divided by 10.
• It increments the value of count by 1 to indicate the presence of another digit.
• It updates the value of the number by dividing it by 10, effectively removing the rightmost digit.
• The loop continues until the number becomes 0, indicating that all digits have been processed.
• Once the while loop is complete, the program prints the value of count, which represents the number of digits in the given number.
• The program ends.

Conclusion

The C program successfully counts the number of digits in a given number using a while loop. By dividing the number by 10 repeatedly until it becomes 0, it iterates through the digits and increments a counter variable. The program then displays the count of digits on the screen.