Logical Operators

Logical Operators

Logical Operators

Sometimes one condition isn't enough. You need to check if someone is old enough AND has a ticket, or if they're an admin OR the owner.

Go gives you three logical operators to combine conditions:

Operator Meaning Example
&& and, both must be true age >= 18 && hasTicket
|| or, at least one true isAdmin || isOwner
! not, flips a boolean !ready
example.go
if age >= 18 && hasID {
    fmt.Println("Welcome")
}

if isAdmin || isOwner || isModerator {
    fmt.Println("Access granted")
}

if !maintenance {
    fmt.Println("System is up")
}

You can combine multiple operators in one expression. Use parentheses to make the grouping clear:

example.go
if (age >= 18 && hasTicket) || isVIP {
    fmt.Println("You're in")
}

Without parentheses, && binds tighter than || (just like * before + in math). But when in doubt, add parentheses to make your intent obvious.

Go also short-circuits: if the left side of && is false, it skips the right side entirely. If the left side of || is true, it skips the right side. This matters when the right side has a function call you might not want to run.

Booleans are already booleans

If you have a bool variable, you don't need to compare it to true:

example.go
if cpuHigh == true { ... } // works, but verbose
if cpuHigh { ... }         // same thing, idiomatic
if !cpuHigh { ... }         // checks for false

Extra == true checks are more typing and more places to typo a variable name. Just use the bool directly.

Mapping conditions to outcomes

When a rule depends on several bools, it helps to lay out every combination. For the exercise below, three inputs (cpuHigh, memoryHigh, diskFull) mean 2 × 2 × 2 = 8 cases, and the rules collapse them into three outcomes:

cpuHigh memoryHigh diskFull result
true true any CRITICAL
true false any WARNING
false true any WARNING
false false true WARNING
false false false OK

A "match any row" structure like this maps directly onto if / else if / else.

>_Exercise

Exercise: System Monitor

You're building a server monitoring alert system. Update the status variable inside checkSystem based on these rules:

If both cpuHigh and memoryHigh are true, set status to "CRITICAL".

If at least one of cpuHigh, memoryHigh, or diskFull is true, set status to "WARNING".

Check for "CRITICAL" before "WARNING", since a critical situation also matches the warning condition.

If nothing is wrong, status stays "OK" (the default).

Examples:

  • checkSystem(true, true, false) → "CRITICAL" (CPU and memory both high)
  • checkSystem(true, false, false) → "WARNING" (only CPU is high)
  • checkSystem(false, false, false) → "OK" (nothing is wrong)
Stuck? Reveal a hint to help you.
Hints (0/3)
Key Takeaway
Next UpWriting reusable code with functions.
Previous
Next