C# - Nested Loops

C# Nested Loops

A nested loop in c# states that a loop inside another loop where the inner loop executes completely for each iteration of the outer loop. The following section shows a few examples to illustrate the nested loops −

Syntax

Following is the syntax of the C# nested for loop statement −

for ( init; condition; increment ) {
   for ( init; condition; increment ) {
      statement(s);
   }
   statement(s);
}

Following is the syntax of the C# nested while loop statement −

while(condition) {
   while(condition) {
      statement(s);
   }
   statement(s);
}

Following is the syntax of the C# nested do...while loop statement minus;

do {
   statement(s);
   do {
      statement(s);
   }
   while( condition );
}
while( condition );

It is important to note that a loop nesting is that you can put any type of loop inside of any other type of loop. For example a for loop can be inside a while loop or vice versa.

Nested for Loop

The following program uses a nested for loop to find the prime numbers from 2 to 100 −

using System;
namespace Loops {
   class Program {
      static void Main(string[] args) {
         /* local variable definition */
         int i, j;
         
         for (i = 2; i < 100; i++) {
            for (j = 2; j <= (i / j); j++)
            if ((i % j) == 0) break; // if factor found, not prime
            if (j > (i / j)) Console.WriteLine("{0} is prime", i);
         }
         Console.ReadLine();
      }
   }
} 

Output

When the above code is compiled and executed, it produces the following result −

2 is prime
3 is prime
5 is prime
7 is prime
11 is prime
13 is prime
17 is prime
19 is prime
23 is prime
29 is prime
31 is prime
37 is prime
41 is prime
43 is prime
47 is prime
53 is prime
59 is prime
61 is prime
67 is prime
71 is prime
73 is prime
79 is prime
83 is prime
89 is prime
97 is prime

Nested while Loops

The following program uses a nested while loop to find the prime numbers from 2 to 100 −

using System;
namespace Loops {
   class Program {
      static void Main(string[] args) {
         int i = 2, j;
         
         // Outer loop
         while (i < 100) {
            j = 2;
            // Inner loop
            while (j <= (i / j)) {
               if ((i % j) == 0)
                  // If factor found, not prime
                  break;
               j++;
            }
            if (j > (i / j)) 
               Console.WriteLine("{0} is prime", i);
            i++;
         }
         Console.ReadLine();
      }
   }
}

Output

The above code generates the following output −

2 is prime
3 is prime
5 is prime
7 is prime
11 is prime
13 is prime
17 is prime
19 is prime
23 is prime
29 is prime
31 is prime
37 is prime
41 is prime
43 is prime
47 is prime
53 is prime
59 is prime
61 is prime
67 is prime
71 is prime
73 is prime
79 is prime
83 is prime
89 is prime
97 is prime

Nested do while Loops

The following program uses a nested Do-while loop to find the prime numbers from 2 to 100 −

using System;
namespace Loops {
   class Program {
      static void Main(string[] args) {
         int i = 2, j;
         
         // Outer loop
         do {
            j = 2;
            
            // Inner loop
            do {
               if ((i % j) == 0)
                  break; // If factor found, not prime
               j++;
            } while (j <= (i / j));

            if (j > (i / j)) 
               Console.WriteLine("{0} is prime", i);

            i++;
         } while (i < 100);

         Console.ReadLine();
      }
   }
}

Output

Following is the output of the above code −

2 is prime
3 is prime
5 is prime
7 is prime
11 is prime
13 is prime
17 is prime
19 is prime
23 is prime
29 is prime
31 is prime
37 is prime
41 is prime
43 is prime
47 is prime
53 is prime
59 is prime
61 is prime
67 is prime
71 is prime
73 is prime
79 is prime
83 is prime
89 is prime
97 is prime