How to Get the Length of an Integer in Ruby?

You can get the length of an integer in Ruby in any of the following ways:

• Converting to Array and Checking the length;
• Converting to String and Checking the length;
• Looping and Removing Digits Off the End;
• Calculating the Number of Digits.

Converting to Array and Checking the length

If you have a positive integer, you can do the following:

1. Convert integer to an array of digits (using Integer#digits);
2. Call the Array#length (or Array#size) method on the resulting array of digits.

# Ruby 2.4+
print 12345.digits.length #=> 5

If the number can potentially be negative, then you must first get the absolute value of the integer:

# Ruby 2.4+
print -12345.abs.digits.length #=> 5

To make it reusable, you could make this into a function, for example, like so:

# Ruby 2.4+
def num_length(num)
    num.abs.digits.length
end

print num_length(0) #=> 1
print num_length(12345) #=> 5
print num_length(-12345) #=> 5
print num_length(9999999999999999999999999) #=> 25
print num_length(-9999999999999999999999999) #=> 25

Converting to String and Checking the length

If you have a positive integer, you can do the following:

1. Convert integer to string (using Integer#to_s);
2. Call the String#length method on the resulting string.

print 12345.to_s.length #=> 5

If the number can potentially be negative, then you must first get the absolute value of the integer:

print -12345.abs.to_s.length #=> 5

To make it reusable, you could make this into a function, for example, like so:

def num_length(num)
    num.abs.to_s.length
end

print num_length(0) #=> 1
print num_length(12345) #=> 5
print num_length(-12345) #=> 5
print num_length(9999999999999999999999999) #=> 25
print num_length(-9999999999999999999999999) #=> 25

Looping and Removing Digits Off the End

If you have a positive or a negative integer, you can do the following:

1. Create a loop, and remove the last digit from the number in each iteration till there are no digits left;
2. In each iteration, increment a counter, which would give the total number of digits in the number.

def num_length(num)
    len = 0
    loop do
        num = (num.abs / 10).to_i
        len += 1

        if num == 0
            break
        end
    end

    len
end

print num_length(0) #=> 1
print num_length(12345) #=> 5
print num_length(-12345) #=> 5
print num_length(9999999999999999999999999) #=> 25
print num_length(-9999999999999999999999999) #=> 25

Calculating the Number of Digits

You should use this method with caution as it may give you the wrong result for really large numbers (such as 9999999999999999999999999).

If you have a positive integer, you can do the following:

1. Calculate the log10 of the number, convert it to an integer and add 1 to the result;
2. If the number is 0, then return 1 as a count (because log10(0) equals -Infinity).

num = 12345
print num == 0 ? 1 : Math.log10(num).to_i + 1 #=> 5

If the number can potentially be negative, then you must first get the absolute value of the integer:

num = -12345
print num == 0 ? 1 : Math.log10(num.abs).to_i + 1 #=> 5

To make it reusable, you could make this into a function, for example, like so:

def num_length(num)
    num == 0 ? 1 : Math.log10(num.abs).to_i + 1
end

print num_length(0) #=> 1
print num_length(12345) #=> 5
print num_length(-12345) #=> 5

// this may give wrong result for really large numbers
print num_length(9999999999999999999999999) #=> 26
print num_length(-9999999999999999999999999) #=> 26