C# For Loop - Complete Guide
Introduction to For Loops
The for loop in C# is a control flow statement that executes a block of code repeatedly for a specified number of iterations. It is most useful when the number of iterations is known beforehand.
The for loop consists of three parts: initialization, condition, and iteration. This structure makes it ideal for iterating through arrays, collections, and performing counter-based tasks.
Basic For Loop Syntax
A for loop has initialization, condition, and iteration expressions inside parentheses:
Example
using System;
namespace ForLoopExample
{
class Program
{
static void Main(string[] args)
{
// Print numbers 1 to 5
for (int i = 1; i <= 5; i++)
{
Console.WriteLine("Number: " + i);
}
// Counting backwards
Console.WriteLine("\nCounting backwards:");
for (int i = 5; i >= 1; i--)
{
Console.WriteLine("Number: " + i);
}
// Step by 2
Console.WriteLine("\nEven numbers between 0 and 10:");
for (int i = 0; i <= 10; i += 2)
{
Console.WriteLine("Even: " + i);
}
// Multiples of 5
Console.WriteLine("\nMultiples of 5:");
for (int i = 5; i <= 25; i += 5)
{
Console.WriteLine("Multiple: " + i);
}
// Calculate sum
int sum = 0;
for (int i = 1; i <= 10; i++)
{
sum += i;
}
Console.WriteLine($"\nSum of numbers 1 to 10: {sum}");
}
}
}Output
Number: 1 Number: 2 Number: 3 Number: 4 Number: 5 Counting backwards: Number: 5 Number: 4 Number: 3 Number: 2 Number: 1 Even numbers between 0 and 10: Even: 0 Even: 2 Even: 4 Even: 6 Even: 8 Even: 10 Multiples of 5: Multiple: 5 Multiple: 10 Multiple: 15 Multiple: 20 Multiple: 25 Sum of numbers 1 to 10: 55
For Loop with Arrays and Collections
For loops are often used with arrays and collections:
Example
using System;
namespace ForLoopWithArrays
{
class Program
{
static void Main(string[] args)
{
int[] numbers = { 10, 20, 30, 40, 50 };
Console.WriteLine("Array elements:");
for (int i = 0; i < numbers.Length; i++)
{
Console.WriteLine($"Index {i}: {numbers[i]}");
}
// Calculate stats
int[] scores = { 85, 92, 78, 90, 88 };
int total = 0, highest = scores[0], lowest = scores[0];
for (int i = 0; i < scores.Length; i++)
{
total += scores[i];
if (scores[i] > highest) highest = scores[i];
if (scores[i] < lowest) lowest = scores[i];
}
double average = (double)total / scores.Length;
Console.WriteLine($"\nStats - Total: {total}, Average: {average:F1}, Highest: {highest}, Lowest: {lowest}");
// 2D array
int[,] matrix = { { 1, 2, 3 }, { 4, 5, 6 }, { 7, 8, 9 } };
Console.WriteLine("\n2D Array elements:");
for (int row = 0; row < matrix.GetLength(0); row++)
{
for (int col = 0; col < matrix.GetLength(1); col++)
{
Console.Write($"{matrix[row, col]} ");
}
Console.WriteLine();
}
// Strings
string text = "Hello";
Console.WriteLine("\nString characters:");
for (int i = 0; i < text.Length; i++)
{
Console.WriteLine($"Character {i}: '{text[i]}' (ASCII: {(int)text[i]})");
}
// Reverse string
string reversed = "";
for (int i = text.Length - 1; i >= 0; i--)
{
reversed += text[i];
}
Console.WriteLine($"\nOriginal: {text}, Reversed: {reversed}");
}
}
}Output
Array elements: Index 0: 10 Index 1: 20 Index 2: 30 Index 3: 40 Index 4: 50 Stats - Total: 433, Average: 86.6, Highest: 92, Lowest: 78 2D Array elements: 1 2 3 4 5 6 7 8 9 String characters: Character 0: 'H' (ASCII: 72) Character 1: 'e' (ASCII: 101) Character 2: 'l' (ASCII: 108) Character 3: 'l' (ASCII: 108) Character 4: 'o' (ASCII: 111) Original: Hello, Reversed: olleH
Advanced For Loop Techniques
For loops can be extended to handle more complex patterns:
Example
using System;
namespace AdvancedForLoop
{
class Program
{
static void Main(string[] args)
{
// Multiple variables
for (int i = 0, j = 10; i < j; i++, j--)
{
Console.WriteLine($"i: {i}, j: {j}");
}
// Infinite loop with break
int counter = 0;
for (;;)
{
Console.WriteLine("Iteration: " + (counter + 1));
if (++counter >= 5) break;
}
// Multiplication table
for (int i = 1; i <= 5; i++)
{
for (int j = 1; j <= 5; j++)
{
Console.Write($"{i * j,4}");
}
Console.WriteLine();
}
// Continue statement
for (int i = 1; i <= 10; i++)
{
if (i % 2 == 0) continue;
Console.WriteLine("Odd: " + i);
}
// Divisible by 3 or 5
for (int i = 1; i <= 20; i++)
{
if (i % 3 == 0 || i % 5 == 0)
{
Console.WriteLine($"{i} is divisible by 3 or 5");
}
}
// External control
bool shouldContinue = true;
for (int i = 1; shouldContinue && i <= 100; i++)
{
Console.WriteLine("Processing: " + i);
if (i >= 7) shouldContinue = false;
}
}
}
}Output
i: 0, j: 10 i: 1, j: 9 i: 2, j: 8 i: 3, j: 7 i: 4, j: 6 Iteration: 1 Iteration: 2 Iteration: 3 Iteration: 4 Iteration: 5 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 Odd: 1 Odd: 3 Odd: 5 Odd: 7 Odd: 9 3 is divisible by 3 or 5 5 is divisible by 3 or 5 6 is divisible by 3 or 5 9 is divisible by 3 or 5 10 is divisible by 3 or 5 12 is divisible by 3 or 5 15 is divisible by 3 or 5 18 is divisible by 3 or 5 20 is divisible by 3 or 5 Processing: 1 Processing: 2 Processing: 3 Processing: 4 Processing: 5 Processing: 6 Processing: 7