C program to Count the digits of a number

Given a number N, write a C program to find the count of digits in the number N. 

Examples:

Input: N = 12345 
Output: 5 
Explanation: The count of digit in 12345 = 5
 
Input: N = 23451452 
Output: 8 
Explanation: The count of digits in 23451452 = 8

Methods to Count Digits of a Number

There are a few methods to count the digits of a number mentioned below:

• Using Loops
• Logarithmic Approach
• Using Recursion
• Using Repeated Multiplication
• By Dividing with Powers of Two

1. Using Loops

The count of digits in a number can be found efficiently in a few steps:

1. Remove the last digit of the number by dividing it by 10.
2. Increment the count of digits by 1.
3. Keep repeating steps 1 and 2 until the value of N becomes 0. In this case, there will be no more digits left in the number to count.

Example:

C

// C Program to Find Count of
// Digits in a Number
// Using Loops
#include <stdio.h>

// Find the count of digits
int findCount(int n)
{
    int count = 0;

    // Remove last digit from number
    // till number is 0
    while (n != 0) {

        // Increment count
        count++;
        n /= 10;
    }

    // return the count of digit
    return count;
}

// Driver program
int main()
{
    int n = 98562;
    printf("Count of digits in %d = %d\n", n, findCount(n));
    return 0;
}

Output

Count of digits in 98562 = 5

The complexity of the above method

Time complexity: O(D), where D is the count of digits in the number N. 

Auxiliary Space: O(1)

2. Logarithmic Approach

Below is the C program to count the number of digits in a number without using a loop:

C

// C Program to Count the Number
// Of Digits in a Number
// Using Logarithmic Approach
#include <math.h>
#include <stdio.h>

// Driver code
int main()
{
    int n = 98562;
    int count = 0;

    count = (n == 0) ? 1 : log10(n) + 1;
    printf("Count of digits in %d = %d\n", n, count);
    return 0;
}

Output

Count of digits in 98562 = 5

3. Using Recursion

Below is the C program to count the number of digits using functions:

C

// C Program to Count the Number
// Of digits in a number
// Using Recursion
#include <stdio.h>

int Count_Of_Digits(int n)
{
    static int Count = 0;

    if (n > 0) {
        Count = Count + 1;
        Count_Of_Digits(n / 10);
    }

    return Count;
}

// Driver code
int main()
{
    int n = 98562, Count = 0;
    Count = Count_Of_Digits(n);

    printf("Count of digits in %d = %d\n", n, Count);
    return 0;
}

Output

Count of digits in 98562 = 5

4. Using Repeated Multiplication

Below is the C program to count the number of digits in a number using repeated multiplication:

C

// C Program to Count the Number
// Of Digits in a Number
// Using Repeated Multiplication
#include <stdio.h>

// function to find the count
// the number
int findCount(unsigned int n)
{
    unsigned int count = 0;
    unsigned int temp = 1;
    while (temp <= n) {
        count++;
        temp *= 10;
    }
    return count;
}

// Driver code
int main()
{
    unsigned int n = 98523, digits;

    // call function to count digit
    digits = findCount(n);
    printf("Count of digits in %d = %d\n", n, digits);
    return 0;
}

Output

Count of digits in 98523 = 5

5. By Dividing with Powers of Two

Below is the C program to count the number of digits in a number by dividing with powers of two:

C

// C Program to Count the Number
// Of Digits in a Number
// By Dividing with Powers of Two
#include <stdio.h>

int findCount(unsigned int n)
{
    int count = 1;

    if (n >= 100000000) {
        count += 8;
        n /= 100000000;
    }

    if (n >= 10000) {
        count += 4;
        n /= 10000;
    }

    if (n >= 100) {
        count += 2;
        n /= 100;
    }

    if (n >= 10) {
        count += 1;
    }

    return count;
}

// Driver code
int main()
{
    unsigned int n = 98532, digits;

    // call function to count digit
    digits = findCount(n);

    printf("Count of digits in %d = %d\n", n, digits);
    return 0;
}

Output

Count of digits in 98532 = 5