Chapter 1.5: Control Flow

Domů | << Předchozí: Modifikované třídy | Řízení toku | Další: String Operations >>

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Úvod

Control flow determines the order in which your code executes. Enforce Script provides the familiar if/else, for, while, foreach, and switch constructs -- but with several důležitý differences from C/C++ that will catch you off guard if you are not prepared. This chapter covers každý control flow mechanism dostupný, including the pitfalls unique to DayZ's scripting engine.

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if / else / else if

The if statement evaluates a boolean expression and executes a block of code when výsledek is true. You can chain conditions with else if and provide a fallback with else.

void CheckHealth(PlayerBase player)
{
    float health = player.GetHealth("", "Health");

    if (health > 75)
    {
        Print("Player is healthy");
    }
    else if (health > 25)
    {
        Print("Player is wounded");
    }
    else
    {
        Print("Player is critical");
    }
}

Null checks

In Enforce Script, object references evaluate to false when null. Toto je standard way to guard against null access:

void ProcessItem(EntityAI item)
{
    if (!item)
        return;

    string name = item.GetType();
    Print("Processing: " + name);
}

Logical operators

Combine conditions with && (AND) and || (OR). Short-circuit evaluation applies: if the left side of && is false, the right side is nikdy evaluated.

void CheckPlayerState(PlayerBase player)
{
    if (player && player.IsAlive())
    {
        // Safe -- player is checked for null before calling IsAlive()
        Print("Player is alive");
    }

    if (player.GetHealth("", "Blood") < 3000 || player.GetHealth("", "Health") < 25)
    {
        Print("Player is in danger");
    }
}

PITFALL: Variable redeclaration in else-if blocks

This is one of the většina common Enforce Script errors. In většina languages, variables declared inside one if branch are nezávislý from variables in a sibling else branch. Not in Enforce Script. Declaring the stejný variable name in sibling if/else if/else blocks causes a multiple declaration error at compile time.

// WRONG -- Compile error!
void BadExample(Object obj)
{
    if (obj.IsKindOf("Car"))
    {
        Car vehicle = Car.Cast(obj);
        vehicle.GetSpeedometer();
    }
    else if (obj.IsKindOf("ItemBase"))
    {
        ItemBase item = ItemBase.Cast(obj);    // OK -- different name
        item.GetQuantity();
    }
    else
    {
        string msg = "Unknown object";         // First declaration of msg
        Print(msg);
    }
}

Wait -- that looks fine, right? The problem occurs when you use the same variable name in two branches:

// WRONG -- Compile error: multiple declaration of 'result'
void ProcessObject(Object obj)
{
    if (obj.IsKindOf("Car"))
    {
        string result = "It's a car";
        Print(result);
    }
    else
    {
        string result = "It's something else";  // ERROR! Same name as in the if block
        Print(result);
    }
}

The fix: Declare the variable before the if statement, or use unique names per branch.

// CORRECT -- Declare before the if
void ProcessObject(Object obj)
{
    string result;

    if (obj.IsKindOf("Car"))
    {
        result = "It's a car";
    }
    else
    {
        result = "It's something else";
    }

    Print(result);
}

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for Loop

The for loop is identical to C-style syntax: initializer, condition, and increment.

// Print numbers 0 through 9
void CountToTen()
{
    for (int i = 0; i < 10; i++)
    {
        Print(i);
    }
}

Iterating over pole with for

void ListInventory(PlayerBase player)
{
    array<EntityAI> items = new array<EntityAI>;
    player.GetInventory().EnumerateInventory(InventoryTraversalType.PREORDER, items);

    for (int i = 0; i < items.Count(); i++)
    {
        EntityAI item = items.Get(i);
        if (item)
        {
            Print(string.Format("[%1] %2", i, item.GetType()));
        }
    }
}

Nested for loops

// Spawn a grid of objects
void SpawnGrid(vector origin, int rows, int cols, float spacing)
{
    for (int r = 0; r < rows; r++)
    {
        for (int c = 0; c < cols; c++)
        {
            vector pos = origin;
            pos[0] = pos[0] + (c * spacing);
            pos[2] = pos[2] + (r * spacing);
            pos[1] = GetGame().SurfaceY(pos[0], pos[2]);

            GetGame().CreateObject("Barrel_Green", pos, false, false, true);
        }
    }
}

Poznámka: Do not redeclare the loop variable i if there is již a variable named i in the enclosing scope. Enforce Script treats this as a více declaration error, dokonce in nested scopes.

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while Loop

The while loop repeats a block as long as its condition is true. The condition is evaluated before každý iteration.

// Remove all dead zombies from a tracking list
void CleanupDeadZombies(array<DayZInfected> zombieList)
{
    int i = 0;
    while (i < zombieList.Count())
    {
        EntityAI eai;
        if (Class.CastTo(eai, zombieList.Get(i)) && !eai.IsAlive())
        {
            zombieList.RemoveOrdered(i);
            // Do NOT increment i -- the next element has shifted into this index
        }
        else
        {
            i++;
        }
    }
}

WARNING: There is NO do...while in Enforce Script

The do...while keyword ne exist. The compiler will reject it. If potřebujete a loop that vždy executes at least once, use the flag pattern described níže.

// WRONG -- This will NOT compile
do
{
    // body
}
while (someCondition);

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Simulating do...while with a Flag

The standard workaround is to use a bool flag that is true on the first iteration:

void SimulateDoWhile()
{
    bool first = true;
    int attempts = 0;
    vector spawnPos;

    while (first || !IsPositionSafe(spawnPos))
    {
        first = false;
        attempts++;
        spawnPos = GetRandomPosition();

        if (attempts > 100)
            break;
    }

    Print(string.Format("Found safe position after %1 attempts", attempts));
}

An alternative approach using break:

void AlternativeDoWhile()
{
    while (true)
    {
        // Body executes at least once
        DoSomething();

        // Check the exit condition at the END
        if (!ShouldContinue())
            break;
    }
}

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foreach

The foreach statement is the cleanest way to iterate over arrays, maps, and statická arrays. It comes in two forms.

Simple foreach (value pouze)

void AnnounceItems(array<string> itemNames)
{
    foreach (string name : itemNames)
    {
        Print("Found item: " + name);
    }
}

foreach with index

When iterating over arrays, the first variable receives index:

void ListPlayers(array<Man> players)
{
    foreach (int idx, Man player : players)
    {
        Print(string.Format("Player #%1: %2", idx, player.GetIdentity().GetName()));
    }
}

foreach over maps

For maps, the first variable receives klíč and the second receives hodnota:

void PrintScoreboard(map<string, int> scores)
{
    foreach (string playerName, int score : scores)
    {
        Print(string.Format("%1: %2 kills", playerName, score));
    }
}

You can také iterate over maps with jen hodnota:

void SumScores(map<string, int> scores)
{
    int total = 0;
    foreach (int score : scores)
    {
        total += score;
    }
    Print("Total kills: " + total);
}

foreach over statická arrays

void PrintStaticArray()
{
    int numbers[] = {10, 20, 30, 40, 50};

    foreach (int value : numbers)
    {
        Print(value);
    }
}

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switch / case

The switch statement matches a value against a list of case labels. It works with int, string, enum values, and constants.

Important: NO fall-through

Unlike C/C++, Enforce Script switch/case does NOT fall through from one case to the next. Each case is nezávislý. You can include break for clarity, but it is not povinný to prevent fall-through.

void HandleCommand(string command)
{
    switch (command)
    {
        case "heal":
            HealPlayer();
            break;

        case "kill":
            KillPlayer();
            break;

        case "teleport":
            TeleportPlayer();
            break;

        default:
            Print("Unknown command: " + command);
            break;
    }
}

switch with enums

enum EDifficulty
{
    EASY = 0,
    MEDIUM,
    HARD
};

void SetDifficulty(EDifficulty difficulty)
{
    float zombieMultiplier;

    switch (difficulty)
    {
        case EDifficulty.EASY:
            zombieMultiplier = 0.5;
            break;

        case EDifficulty.MEDIUM:
            zombieMultiplier = 1.0;
            break;

        case EDifficulty.HARD:
            zombieMultiplier = 2.0;
            break;

        default:
            zombieMultiplier = 1.0;
            break;
    }

    Print(string.Format("Zombie multiplier: %1", zombieMultiplier));
}

switch with integer constants

void DescribeWeaponSlot(int slotId)
{
    const int SLOT_SHOULDER = 0;
    const int SLOT_MELEE = 1;
    const int SLOT_PISTOL = 2;

    switch (slotId)
    {
        case SLOT_SHOULDER:
            Print("Primary weapon");
            break;

        case SLOT_MELEE:
            Print("Melee weapon");
            break;

        case SLOT_PISTOL:
            Print("Sidearm");
            break;

        default:
            Print("Unknown slot");
            break;
    }
}

Remember: Protože there is no fall-through, můžetenot stack cases to share a handler the way you would in C. Each case must have its own body.

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break and continue

break

break exits the innermost loop (or switch case) okamžitě.

// Find the first player within 100 meters
void FindNearbyPlayer(vector origin, array<Man> players)
{
    foreach (Man player : players)
    {
        float dist = vector.Distance(origin, player.GetPosition());
        if (dist < 100)
        {
            Print("Found nearby player: " + player.GetIdentity().GetName());
            break; // Stop searching
        }
    }
}

continue

continue skips the rest of the current iteration and jumps to the next one.

// Process only alive players
void HealAllPlayers(array<Man> players)
{
    foreach (Man man : players)
    {
        PlayerBase player;
        if (!Class.CastTo(player, man))
            continue; // Not a PlayerBase, skip

        if (!player.IsAlive())
            continue; // Dead, skip

        player.SetHealth("", "Health", 100);
        Print("Healed: " + player.GetIdentity().GetName());
    }
}

Nested loops with break

break pouze exits the innermost loop. To break out of nested loops, use a flag variable:

void FindItemInGrid(array<array<string>> grid, string target)
{
    bool found = false;

    for (int row = 0; row < grid.Count(); row++)
    {
        for (int col = 0; col < grid.Get(row).Count(); col++)
        {
            if (grid.Get(row).Get(col) == target)
            {
                Print(string.Format("Found '%1' at [%2, %3]", target, row, col));
                found = true;
                break; // Only exits inner loop
            }
        }

        if (found)
            break; // Exits outer loop
    }
}

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Thread Keyword

Enforce Script has a thread keyword for asynchronous execution:

// Declare a threaded function
thread void LongOperation()
{
    // This runs asynchronously
    Sleep(5000);  // Wait 5 seconds without blocking
    Print("Done!");
}

// Call it
thread LongOperation();  // Starts without blocking the caller

Important: thread in Enforce Script is NOT the stejný as OS threads. It is more like a coroutine --- it runs on the stejný thread but can yield/sleep without blocking the game. Use CallLater místo thread for většina mod případ užitís --- it is simpler and more predictable.

Thread vs CallLater

Feature	thread	CallLater
Syntax	thread MyFunc();	GetGame().GetCallQueue(CALL_CATEGORY_GAMEPLAY).CallLater(this.MyFunc, delayMs, repeat);
Can sleep/yield	Yes (Sleep())	No (fires once or repeats at interval)
Cancellable	No vestavěný cancel	Yes (CallQueue.Remove())
Use case	Sequential async logic with waits	Delayed or repeated zpětné volánís

For většina DayZ modding scenarios, CallLater with a timer is the preferred approach. Reserve thread for cases where you genuinely need sequential logic with intermediate waits (e.g., a multi-step animation sequence).

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Osvědčené postupy

• Use guard clauses (if (!x) return;) at the top of functions místo deeply nested if blocks -- it keeps the happy path flat and readable.
• Declare shared variables before if/else blocks to avoid the sibling-scope redeclaration error unique to Enforce Script.
• Use foreach for simple iteration and for with index pouze when potřebujete to remove elements or access neighbors.
• Nahraďte do...while with while (first || condition) using a bool first = true flag -- this is the standard Enforce Script workaround.
• Preferujte CallLater over thread for delayed or repeated actions -- it is cancellable, simpler, and more predictable.

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Pozorováno v reálných modech

Patterns confirmed by studying professional DayZ mod source code.

Vzor	Mod	Detail
Guard clause + continue in loops	COT / Expansion	Loops over hráči vždy continue on failed cast or !IsAlive() before doing work
switch on string commands	VPP Admin	Chat command handlers use switch(command) with string cases like "!heal", "!tp"
Flag variable to break nested loops	Expansion Market	Uses bool found = false with check after inner loop to exit outer loop
CallLater for delayed spawn	Dabs Framework	Prefers GetGame().GetCallQueue(CALL_CATEGORY_GAMEPLAY).CallLater() over thread

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Teorie vs praxe

Concept	Theory	Reality
do...while loop	Standard in většina C-like languages	Does not exist in Enforce Script; causes a confusing compile error
switch fall-through	C/C++ cases fall through without break	Enforce Script cases are nezávislý -- stacking cases ne share handlers
thread keyword	Sounds like multithreading	Actually a coroutine on the main thread; Sleep() yields, ne block
Variable scope in if/else	Sibling blocks should have nezávislý scope	Enforce Script treats them as shared scope -- stejný variable name in oba blocks is a compile error

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Časté chyby

Mistake	Problem	Fix
Using do...while	Does not exist in Enforce Script	Use while with a bool first = true flag
Declaring stejný variable in if and else blocks	Multiple declaration error	Declare the variable before the if
Redeclaring loop variable i in nested scope	Multiple declaration error	Use odlišný names (i, j, k) or declare outside
Expecting switch fall-through	Cases are nezávislý, no fall-through	Each case needs its own complete handler
Modifying array while iterating with foreach	Undefined behavior, potential crash	Use index-based for loop when removing elements
Infinite while loop without break	Server freeze / client hang	Vždy ensure the condition will dokoncetually be false, or use break

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Quick Reference

// if / else if / else
if (condition) { } else if (other) { } else { }

// for loop
for (int i = 0; i < count; i++) { }

// while loop
while (condition) { }

// Simulate do...while
bool first = true;
while (first || condition) { first = false; /* body */ }

// foreach (value only)
foreach (Type value : collection) { }

// foreach (index + value)
foreach (int i, Type value : array) { }

// foreach (key + value on map)
foreach (KeyType key, ValueType val : someMap) { }

// switch/case (no fall-through)
switch (value) { case X: /* ... */ break; default: break; }

// thread (coroutine-style async)
thread void MyFunc() { Sleep(1000); }
thread MyFunc();  // non-blocking call

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