3.2 Loops

The fundamental way to repeat code.

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📌 1. for Loop

Use for when you know how many times to iterate.

for (int i = 0; i < 5; i++)
{
    Console.WriteLine("Iteration: " + i);
}

• Structure: for(initialization; condition; increment/decrement)

• Executes as long as the condition is true.

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📌 2. while Loop

Use while when you want to repeat until a condition becomes false.

int count = 0;
 
while (count < 5)
{
    Console.WriteLine("Count: " + count);
    count++;
}

• The condition is checked before each iteration.

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📌 3. do-while Loop

Similar to while, but executes at least once because the condition is checked after the loop.

int count = 0;
 
do
{
    Console.WriteLine("Count: " + count);
    count++;
} while (count < 5);

• Use when the loop must run at least once.

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📌 4. foreach Loop

Use foreach to iterate over collections/arrays.

string[] names = { "Alice", "Bob", "Charlie" };
 
foreach (string name in names)
{
    Console.WriteLine(name);
}

• Read-only access to elements.

• Cannot modify the collection itself inside foreach.

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📌 5. Loop Control Keywords

break

Exits the loop immediately.

for (int i = 0; i < 10; i++)
{
    if (i == 5) break;
    Console.WriteLine(i); // prints 0..4
}

continue

Skips the rest of the current iteration and moves to the next.

for (int i = 0; i < 5; i++)
{
    if (i == 2) continue;
    Console.WriteLine(i); // prints 0,1,3,4
}

goto

Rarely used, jumps to a labeled statement. Use sparingly.

int i = 0;
start:
Console.WriteLine(i);
i++;
if (i < 5) goto start;

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📌 6. Nested Loops

Loops can be nested inside each other.

for (int i = 1; i <= 3; i++)
{
    for (int j = 1; j <= 2; j++)
    {
        Console.WriteLine($"i={i}, j={j}");
    }
}

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📌 7. Summary Table

Loop Type	Check Condition	Usage
for	Before	Known number of iterations
while	Before	Condition-controlled
do-while	After	Must run at least once
foreach	N/A	Iterate over collection

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✅ Tip:

• Use for or while for numeric/index-based loops.

• Use foreach for arrays, lists, or collections.

• Use break and continue to control loop flow.