In the context of puzzles such as this:
Write a program that outputs all possibilities to put + or - or nothing between the numbers 1,2,…,9 (in this order) such that the result is 100. For example 1 + 2 + 3 - 4 + 5 + 6 + 78 + 9 = 100.
Is there a name for the "nothing"-operation between 7 and 8?
What it would do is I think: let a,b be positive integers
$a$ nothing $b= a\times 10 +b$
Also if you think this belongs to a special Tag please edit the Tag in there.
It's called concatenation. And it's not $a \times 10 + b$. That fails for numbers with more than one digit.
The correct formula is $a \cdot 10^{1 + \lfloor\log_{10}(b)\rfloor} + b$ where we define $\log_{10}(0) = 0$.