For loops in C#
A for loop is one of the most commonly used control structures in C#. It lets you repeat a block of code a specific number of times — perfect for working with lists, counting, or performing the same action multiple times.
Basic syntax
for (int i = 0; i < 5; i++)
{
Console.WriteLine($"Round number: {i}");
}
Output:
Round number: 0
Round number: 1
Round number: 2
Round number: 3
Round number: 4
A for loop consists of three parts:
- Initialization (
int i = 0) — runs once at the start - Condition (
i < 5) — checked before each iteration; the loop stops when it isfalse - Update (
i++) — runs after each iteration
When do you use a for loop?
Use a for loop when you know how many times you want to repeat something:
// Print the numbers 1 to 10
for (int i = 1; i <= 10; i++)
{
Console.WriteLine(i);
}
// Calculate the sum of the numbers 1 to 100
int sum = 0;
for (int i = 1; i <= 100; i++)
{
sum += i;
}
Console.WriteLine($"The sum is: {sum}"); // 5050
Iterating through an array
One of the most common uses is to iterate through an array:
string[] fruits = { "Apple", "Banana", "Orange", "Mango" };
for (int i = 0; i < fruits.Length; i++)
{
Console.WriteLine($"{i + 1}. {fruits[i]}");
}
Output:
1. Apple
2. Banana
3. Orange
4. Mango
Tip: fruits.Length gives the number of elements. We use i < fruits.Length (not <=) because arrays start from index 0.
Counting backwards
You can also count downwards:
for (int i = 10; i >= 1; i--)
{
Console.WriteLine(i);
}
Console.WriteLine("Start!");
Here we start at 10, check if i >= 1, and subtract 1 after each iteration with i--.
Nested loops (loops within loops)
Sometimes you need a loop inside another loop. This is useful for working with tables or 2D data, for example:
// Print a multiplication table
for (int i = 1; i <= 5; i++)
{
for (int j = 1; j <= 5; j++)
{
Console.Write($"{i * j,4}");
}
Console.WriteLine();
}
Output:
1 2 3 4 5
2 4 6 8 10
3 6 9 12 15
4 8 12 16 20
5 10 15 20 25
Important: Use different variable names in each loop (i and j), otherwise the inner loop will overwrite the outer one.
Break and continue
Two useful keywords to control the flow:
break — stop the loop entirely
for (int i = 0; i < 100; i++)
{
if (i == 5)
{
break; // Stop completely at 5
}
Console.WriteLine(i);
}
// Prints: 0, 1, 2, 3, 4
continue — skip the rest of this iteration
for (int i = 0; i < 10; i++)
{
if (i % 2 != 0)
{
continue; // Skip odd numbers
}
Console.WriteLine(i);
}
// Prints: 0, 2, 4, 6, 8
For loop vs. other loops
C# has several types of loops. Here is a quick comparison:
| Loop type | Best for |
|---|---|
| for | When you know the number of iterations |
| foreach | When you iterate through a collection |
| while | When you don't know how many times |
| do-while | When the code must run at least once |
foreach — the easy alternative
When you just need to iterate through a collection without using an index, foreach is often cleaner:
string[] fruits = { "Apple", "Banana", "Orange" };
// With for:
for (int i = 0; i < fruits.Length; i++)
{
Console.WriteLine(fruits[i]);
}
// With foreach (cleaner):
foreach (string fruit in fruits)
{
Console.WriteLine(fruit);
}
Common mistakes
1. Off-by-one errors
// Error: runs 6 times (0-5) instead of 5
for (int i = 0; i <= 5; i++) { ... }
// Correct: runs 5 times (0-4)
for (int i = 0; i < 5; i++) { ... }
2. Infinite loop
// Don't forget to update the counter!
for (int i = 0; i < 10; ) // Missing i++ — runs forever
{
Console.WriteLine(i);
}
3. Modifying the counter inside the loop
// Avoid this — it makes the code hard to understand
for (int i = 0; i < 10; i++)
{
i += 2; // Confusing! Use a step in the for statement instead
}
Try it yourself
The best way to learn loops is to write them yourself. Try these exercises:
- Print all even numbers from 2 to 20
- Calculate the factorial of 10 (10!)
- Write a program that prints a triangle of stars
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