# Constructing a Float from Integers

QUESTION: I have a integer array of two columns of numbers. I would like to make a floating number, using the integer value of the first column as the integer part of the number and the integer value of the second column as the decimal part of the number. For example:

`    [345, 678] -> 345.678 `

How can I do this in IDL?

ANSWER: The answer to this question came from a variety of sources.

Before I begin with some of the explanations, it is helpful to know a handy algorithm for getting the number of digits in an integer. Apparently, this can be done by recalling your 7th grade math class and the discussion on logarithms. (If your math class occurred more than 40 years ago, you will not need an excuse from the teacher for not remembering this.) The number of digits in an integer can be found by taking the integer part of the base 10 logarithm of the number and adding 1 to it:

```    IDL> int = 45932L
IDL> numDigits = Long(ALOG10(int)) + 1    IDL> Print, numDigits         5
```

So, Mike Galloy's solution takes advantage of this fact. He solves the problem like this.

```    IDL> d = Long(1000 * RandomU(-3L, 2, 5))    IDL> Print, d
897         558          766         589           60         973
37         218          142         984
IDL> num = d[0,*] + d[1,*] / (10.0^(Long(ALOG10(d[1,*])) + 1))
IDL> Print, num       897.558       766.589       60.9730       37.2180
142.984 ```

Bob Stockwell offers a slight variation to this method.

```   IDL> num = d[0,*] + Float(d[1,*]) / 10^StrLen(StrTrim(d[1,*],2))
IDL> Print, num       897.558       766.589       60.9730       37.2180
142.984 ```

Jean Hasban offers this solution.

```   IDL> num = d[0,*] + Float('0.' + StrTrim(d[1,*],2))    IDL> Print, num
897.558       766.589       60.9730       37.2180       142.984 ```