Nested loop means a loop statement inside another loop statement. That is why nested loops are also called as “loop inside loop“.
Syntax for Nested For loop:
for ( initialization; condition; increment ) {
for ( initialization; condition; increment ) {
// statement of inside loop
}
// statement of outer loop
}
Syntax for Nested While loop:
while(condition) {
while(condition) {
// statement of inside loop
}
// statement of outer loop
}
Syntax for Nested Do-While loop:
do{
do{
// statement of inside loop
}while(condition);
// statement of outer loop
}while(condition);
Note: There is no rule that a loop must be nested inside its own type. In fact, there can be any type of loop nested inside any type and to any level.
Syntax:
do{
while(condition) {
for ( initialization; condition; increment ) {
// statement of inside for loop
}
// statement of inside while loop
}
// statement of outer do-while loop
}while(condition);
Below are some examples to demonstrate the use of Nested Loops:
Example 1: Below program uses a nested for loop to print a 2D matrix.
Java
// Java program to print the elements of// a 2 D array or matriximport java.io.*;class GFG { public static void print2D(int mat[][]) { // Loop through all rows for (int i = 0; i < mat.length; i++) { // Loop through all elements of current row for (int j = 0; j < mat[i].length; j++) System.out.print(mat[i][j] + " "); System.out.println(); } } public static void main(String args[]) throws IOException { int mat[][] = { { 1, 2, 3, 4 }, { 5, 6, 7, 8 }, { 9, 10, 11, 12 } }; print2D(mat); }} |
Output:
1 2 3 4 5 6 7 8 9 10 11 12
Example 2: Below program uses a nested for loop to print all prime factors of a number.
Java
// Java program to print all prime factorsimport java.io.*;import java.lang.Math;class GFG { // A function to print all prime factors // of a given number n public static void primeFactors(int n) { // Print the number of 2s that divide n while (n % 2 == 0) { System.out.print(2 + " "); n /= 2; } // n must be odd at this point. So we can // skip one element (Note i = i +2) for (int i = 3; i <= Math.sqrt(n); i += 2) { // While i divides n, print i and divide n while (n % i == 0) { System.out.print(i + " "); n /= i; } } // This condition is to handle the case when // n is a prime number greater than 2 if (n > 2) System.out.print(n); } public static void main(String[] args) { int n = 315; primeFactors(n); }} |
Output:
3 3 5 7
[…] nested loop is a loop within a loop, an inner loop within the body of an outer […]