# Conditional Statements
If you go by the Circom docs, you will be mislead into believing you can quickly create conditional, branching logic using the `if` operand. This is one of the quickest ways to run into an `Error: non-quadratic constrains not allowed!` error. In this section, we will explain the use of Multiplexers in Circom to accomplish branched logic.
### What is a Multiplexer?
A multiplexer, AKA "MUX", is a way to pass multiple signals through a single interface. In electrical engineering, one use of a a multiplexer is to encode many different TV channels into a single stream of data for transmission where the recipient can multiplex between channels for their desired output signal. A multiplexer in an arithmetic circuit is similar- it allows us to take multiple different signals as input, outputting only one chosen input signal.
### Why do I Care About Multiplexers?
Use of `if` statements will quickly cause circuits that have non-quadratic constraints. This is a consequence of trying to compute one branch of logic without trying to compute the other branch. Essentially**, in Circom you must compute all conditional branches of logic and multiplex them to choose the branch you want to proceed with**. This is undoubtedly quite expensive, especially as the need for conditional branching switches from binary "if" statements to something closer to a "switch case". \
Nonetheless, multiplexing between N possibilities is entirely feasible. [Circomlib](https://github.com/iden3/circomlib/tree/master/circuits) contains multiple different MUX types showing up to 4 orders- if you really need more than 16 potential branches, you can explore how the underlying [MultiMux](https://github.com/iden3/circomlib/blob/master/circuits/mux1.circom#L21-L31) template might be resized for your needs. This is likely only in the case of extreme switch cases and would likely be highly inefficient if further conditional / branching logic was applies from this point without R\&D.
### Example
Here we provide an example of how one might (incorrectly) attempt to do conditional logic with a Battleship game's hit detection, as well as the correct way to multiplex conditional logic in this case.
See the *circomlib > Multiplexing* section for more information on the application of multiplexers in the wild.
{% content-ref url="/pages/cwIXxQfPpDUSrkKvGdW2" %}
[Multiplexing](/battlezips/development/circomlib/multiplexing.md)
{% endcontent-ref %}
#### Incorrect Conditional Logic Computation
{% hint style="info" %}
DO NOT DO THIS!!!!
{% endhint %}
```
template HitShip(n) {
signal input ship[3]; // x, y, z to hitscan from
signal input shot[2]; // x, y, to hitscan with
signal output hit; // 0 if not hit, 1 if hit
var _hit = 0;
if (ship[2] == 0) {
for (var i = 0; i < n; i++) {
var _x = (ship[0] + i == shot[0]);
var _y = (ship[1] == shot[1]);
_hit += 1 * (_x == 1 && _y == 1);
}
} else {
for (var i = 0; i < n; i++) {
var _x = (ship[0] == shot[0]);
var _y = (ship[1] + i == shot[1]);
_hit += 1 * (_x == 1 && _y == 1);
}
}
hit <== _hit;
}
```
#### Correct Conditional Logic Computation
{% hint style="info" %}
DO THIS!!!!
{% endhint %}
```
template HitShip(n) {
signal input ship[3]; // x, y, z to hitscan from
signal input shot[2]; // x, y, to hitscan with
signal output hit; // 0 if not hit, 1 if hit
/// COMPUTE HORIZONTAL SHIP ORIENTATION HIT SCAN CASE
var hHit = 0;
for (var i = 0; i < n; i++) {
var _x = (ship[0] + i == shot[0]);
var _y = (ship[1] == shot[1]);
hHit += 1 * (_x == 1 && _y == 1);
}
/// COMPUTE VERTICAL SHIP ORIENTATION HIT SCAN CASE
var vHit = 0;
for (var i = 0; i < n; i++) {
var _x = (ship[0] == shot[0]);
var _y = (ship[1] + i == shot[1]);
vHit += 1 * (_x == 1 && _y == 1);
}
/// MUX TO CONDITIONALLY SELECT SHIP ORIENTATION HIT SCAN
component mux = Mux1();
mux.c[0] <-- hHit; // assign
mux.c[1] <-- vHit;
mux.s <== ship[2];
hit <== mux.out;
}
```
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