Nested if statements and composite conditions

1

Here’s an example to understand nested conditions versus composite conditions

Say we code up this statement

Bring an umbrella if it’s raining but wear a raincoat if it’s windy

Here’s one way to interpret the statement and express it in code

let rainy // boolean true if raining false otherwise
let windy // boolean true if windy false otherwise
let umbrella // boolean true if umbrella needed false otherwise
let raincoat // boolean true if raincoat needed false otherwise

// assume rainy and windy have some values

This expression uses composite conditions

// block 1: composite condition
if(rainy && windy) {
  umbrella=false
  raincoat=true
} else if(rainy && !windy) {
  umbrella=true
  raincoat=false
} else {
  umbrella=false
  raincoat=false
}

This formulation uses nested conditions

// block 2: nested condition
if(rainy) {
  if(windy) {
    umbrella=false
    raincoat=true
  } else {
    umbrella=true
    raincoat=false
 }
} else {
  umbrella=false
  raincoat=false
}

Blocks 1 and 2 are equivalent in that for any given values of rainy and windy the combined values of umbrella and raincoat are the same after either block executes

Now what can we say about the following variants?

// block 3: composite without first else of block 1
if(rainy && windy) {
  umbrella=false
  raincoat=true
} else {
  umbrella=false
  raincoat=false
}

// block 4: nested condition without inner else of block 2
if(rainy) {
  if(windy) {
    umbrella=false
    raincoat=true
  }
} else {
  umbrella=false
  raincoat=false
}

Blocks 3 and 4 are not equivalent to blocks 1 and 2 in that for some values of rainy and windy the combined values of umbrella and raincoat do not match the combined values of the pair after block 1 or block 2

This is apparent since two boolean variables umbrella and raincoat have four possible combinations of values - blocks 1 & 2 establish 3 distinct combinations of values for the variables but blocks 3 and 4 only establish 2 combinations

None of these blocks is right or wrong - each represents some understanding of the English statement - they are however different understandings resulting in different outcomes

2

I think the other thing to think about when faced with nested conditionals (and switch statements too) is not only how do I represent them better while nesting, but also how can I eliminate the nesting or reduce the need for it.

For example,
Given:

let useRaincoat = false;
let useUmbrella = false;

When:

let isWindy = false;
let isRainy = false;

Then:

useRaincoat = (isRainy && isWindy); /* don't use a raincoat */ 
useUmbrella = (isRainy && !isWindy); /* don't use an umbrella */

OR When:

let isWindy = false;
let isRainy = true;

Then:

useRaincoat = (isRainy && isWindy); /* don't use a raincoat */ 
useUmbrella = (isRainy && !isWindy); /* do use an umbrella */

OR When:

let isWindy = true;
let isRainy = true;

Then:

useRaincoat = (isRainy && isWindy); /* do use a raincoat */ 
useUmbrella = (isRainy && !isWindy); /* don't use an umbrella */

And of course you could also make these test functions as well:

function isUmbrellaWeather(isRainy, isWindy){
    return  (isRainy && !isWindy);
}
function isRaincoatWeather(isRainy, isWindy){
    return (isRainy && isWindy);
}

useRaincoat = isRaincoatWeather(true, false); /* don't use a raincoat */
useUmbrella = isUmbrellaWeather(true, false); /* do use an umbrella */

And you could probably refactor those two functions down even further using arrow functions:

const isUmbrellaWeather = (isRainy, isWindy) => isRainy && !isWindy;
const isRaincoatWeather = (isRainy, isWindy) => isRainy && isWindy;
1 Like