Determine if a string is numeric: Difference between revisions

==={{header|QB64}}===

<lang QB64>

Input "Enter a text or a number: ", v$ 'The "$" establishes that this is a string variable. So whatever entered will be stored as

'a string.

If v$ = Str$(Val(v$)) Then 'Str$() converts numeric values to their string counter parts and Val() does the opposite,

'converting strings to their numerical values. By converting the value of whatever is stored

'in v$ to a number and then back to a string it will have either stayed completely the same,

'in which case it is a numeric value (including exponent and hex and oct based numbers) or

'what is returned by the nested Str$() and Val$() functions will be different, in which case

'one, the other, or both returned an error or a truncation of the original string which began

'with numeric characters but was not entirely a number, such as "99, rue de Rivoli".

Print "Your entered a number."

Else

Print "You did not enter a number."

End If

Sleep

System

</lang>

{{out}}

<pre>

Enter a text or a number: 12345

You entered a number.

Enter a text or a number: Four

You did not enter a number.

Enter a text or a number: 99, rue de Rivoli

You did not enter a number.

Enter a text or a number: 9E4

You entered a number.</pre>

NB: While "99, rue de Rivoli" contains a number it is not a number entirely. The Val(v$) in this case would have stopped after it converted the "99" portion of the input, which when converted back to a string and compared to the original input would not result in an equality. 9E4 the program reads as an exponential value.