let interestingNumbers = [
"Prime": [2, 3, 5, 7, 11, 13],
"Fibonacci": [1, 1, 2, 3, 5, 8],
"Square": [1, 4, 9, 16, 25]
]

var largest = 0
for (_, numbers) in interestingNumbers {
 for number in numbers {
    if number > largest {
        largest = number
    }
  }
}

How does this print 25? I am rather new to coding and am still learning so I am trying to get a good handle on how everything works.Could someone please explain this to me?enter code here

CodePudding user response：

for loops take along time to read and understand because their possibilities are infinite—you can vary results wildly with subtle changes. Most of the time, when people use a loop, they should reach for premade named tools, which are built on loops. It's a never-ending process, learning those, but it's axe sharpening, allowing you to remove bugs and communicate more effectively.

The name for this code is max.

for number in numbers {
  if number > largest {
     largest = number
  }
}

The name for this code is flatMap.

for (_, numbers) in interestingNumbers {
 for number in numbers {

Your code is reinventing this wheel:

interestingNumbers.flatMap(\.value).max()

…meaning, "the maximum value found in all of interestingNumbers's values".

CodePudding user response：

The code you posted is a loop inside another loop (also known as nested loops.)

The outer loop loops through the key/value pairs in a dictionary.

The inner loop loops through the array of integers from the value of each dictionary.

See if you can reason out what the inner code does. It's only a few lines. As Larme suggested, maybe you sould add print statements inside the outer inner loops to log what is happening at each step:

let interestingNumbers = [
"Prime": [2, 3, 5, 7, 11, 13],
"Fibonacci": [1, 1, 2, 3, 5, 8],
"Square": [1, 4, 9, 16, 25]
]

var largest = 0
for (key, numbers) in interestingNumbers {
 print("For key \(key) numbers: \(numbers)")
 for number in numbers {
    print("number: \(number)")
    if number > largest {
        print("Replacing previous largest value of \(largest) with \(number)")
        largest = number
    }
  }
}

Then run the program and examine the output carefully.