Why is my GoLang algorithm going on an infinite loop?

Question

I have been trying to solve the problem below in multiple ways (recursively, with the Go-version of do while loop, and with a for loop). But each one of them goes to an infinite loop. I tried using the same solution in JavaScript, and it works perfectly fine. Can someone please help me understand why the solution below is not working/going on an infinite loop?

// Write a function that takes in a number and returns the next number that is divisible by 7
package main                   

func solution9(num int) int {  

        var done bool = false  
        var result int = 0     

        for i := 1; done != true; i++ { 
                if (num + i % 7 == 0) {         
                        result = num + i                
                        done = true                     
                }              
        }                      

        return result          
}

Chris Heald · Accepted Answer · 2019-01-07 22:44:27Z

10

Your issue is operator precedence. The % operator has a higher precedence than the + operator, so if your num is, say, 10, your test is functionally:

10 + (0 % 7) == 0 => false (10)
10 + (1 % 7) == 0 => false (11)
10 + (2 % 7) == 0 => false (12)

etc.

Obviously, for any num > 0, you'll never satisfy the condition. Change your test to (num+i)%7 == 0 and you should find it works as expected.

answered Jan 7, 2019 at 22:44

Chris Heald

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1 Comment

seemcat Over a year ago

You're an angel. Lol. Thank you Chris!

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