D Programming - Nested Loops

D programming language allows to use one loop inside another loop. The following section shows few examples to illustrate the concept.

Syntax

The syntax for a nested for loop statement is as follows −

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

The syntax for a nested while loop statement is as follows −

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

The syntax for a nested do...while loop statement is as follows −

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

}while( condition );

A final note on 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.

Example

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

import std.stdio;
 
int main () {
   /* local variable definition */
   int i, j;
   
   for(i = 2; i<100; i++) {
      for(j = 2; j <= (i/j); j++)
        if(!(i%j)) break; // if factor found, not prime
      if(j > (i/j)) writefln("%d is prime", i);
   }
 
   return 0;
}

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