How to convert an int64 to int in Go?

Issue

In Go, what is the best strategy for converting int64 to int? I am having difficulty comparing the two

package main 

import (
    "math"
    "strings"
    "strconv"
)

type largestPrimeFactor struct {
    N      int
    Result int
}

func main() {
    base := largestPrimeFactor{N:13195}
    max := math.Sqrt(float64(base.N))

    maxStr := strconv.FormatFloat(max, 'E', 'G', 64)
    maxShift := strings.Split(maxStr, ".")[0]
    maxInt, err := strconv.ParseInt(maxShift, 10, 64)

    if (err != nil) {
        panic(err)
    }

on this next line

    for a := 2; a < maxInt; a++ {
        if isPrime(a) {
            if base.N % a == 0 {
                base.Result = a
            }
        }
    }

    println(base)
}

func isPrime(n int) bool {
    flag := false

    max := math.Sqrt(float64(n))

    maxStr := strconv.FormatFloat(max, 'E', 'G', 64)
    maxShift := strings.Split(maxStr, ".")[0]
    maxInt, err := strconv.ParseInt(maxShift, 10, 64)

    if (err != nil) {
        panic(err)
    }

    for a := 2; a < maxInt; a++ {
        if (n % a == 0) {
            flag := true
        }
    }
    return flag
}

Solution

You convert them with a type “conversion”

var a int
var b int64
int64(a) < b

When comparing values, you always want to convert the smaller type to the larger. Converting the other way will possibly truncate the value:

var x int32 = 0
var y int64 = math.MaxInt32 + 1 // y == 2147483648
if x < int32(y) {
// this evaluates to false, because int32(y) is -2147483648

Or in your case to convert the maxInt int64 value to an int, you could use

for a := 2; a < int(maxInt); a++ {

which would fail to execute correctly if maxInt overflows the max value of the int type on your system.

Answered By – JimB

Answer Checked By – Mary Flores (GoLangFix Volunteer)

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