loops

List of Concepts Involved
Topic: Introduction to Iterative statements/Loops
_ Basic^syntax^of^Java^]
_ Variables]
_ Operators]
_ Conditionals^

_ rntrod}ction^to^rterative^statements/Loops]
_ while^loop]
_ for^loop]
_ How^to^choose^between^while^loop^and^for^loop?]
_ do-while^loop]
_ Brea`^`eyword]
_ Contin}e^`eyword]
_ Using^labels^with^contin}e^and^brea`^`eyword

Are^yo}^familiar^with^the^word^loop?^The^simple^dictionary^meaning^of^loop^is^a^str}ct}re,^series,^or^process,^the^
end^of^which^is^connected^to^the^beginning.^The^point^of^foc}s^here^is^that^the^beginning^and^end^are^
connected.^



Pictorially,^yo}^can^vis}alize^a^loop^li`e^this^

Here,^once^the^loop^begins,^end^will^drive^start^and^start^will^drive^end^}ntil^certain^condition^to^brea`^o}t^of^loop^
is^enco}ntered.



Now^that^we^have^}nderstood^the^simple^meaning^of^loop,^let^}s^now^move^to^the^comp}ter^programming^
terms.

rn^comp}ter^programming,^a^loop^is^a^seq}ence^of^instr}ctions^contin}ally^repeated^}ntil^a^certain^condition^is^
reached.^^
Cracking the Coding Interview in JAVA - Foundation
Topic: The while loop
Assume this scenario, someone comes up to you and says “I want you to give me a program that can give me 
all the numbers between , and ,0000”@ In such a situation, writing all the numbers from , to ,0000 isn’t a feasible 
solution@ Can you connect the dots now? 

Yes, that’s where the concept of loops comes in@ 2oops help you perform a task repeatedly until a certain 
condition is met@ In our example, the task would be to print the value of the number, and the till it is less than 
,0000@K
We have the following types of iterative statements - J
+? The while loopJ
1? The for loopJ
*? The do-while loop

A while loop is a loop that runs through its body, known as a while statement, as long as a predetermined 
condition is evaluated as true@



Syntax

whi e (condition) 

	statement;

K
Let us understand the working of while loop with the help of this simple
example - 



Q- Print the first ,0 natural numbers@ 



To accomplish this-J
+? We declare a variable ‘i’ which denotes the current number@ We initialize it with the value , (as you already 
know, the first natural numberb@J
1? In the while loop, we put a condition that makes the loop run till the value of the variable i doesn’t exceed ,0@J
*? Finally, we print the value of the variable ‘i’ and then increment it by ,@K
Code



int i = 1;

whi e (i ≤ 10) {

 System.out.print(i + “ “);

	 i = i + 1;

h 



Output - 1 2 3 4 5 6 7 8 9 10
Cracking the Coding Interview in JAVA - Foundation
Topic: For loop
Try theIe H
$A Print the sum of the first ‘n’ natural numbers using a for loop, where n is the input.D
GA Write a short program that prints each number from % to %00 on a new line. 
E
 For each multiple of 3, print "Fizz" instead of the number.E
 For each multiple of 5, print "Buzz" instead of the number. E
 For numbers which are multiples of both 3 and 5, print "FizzBuzz" instead of the number.

This is the most widely used loop amongst all.E
The advantage of a for loop is we know exactly how many times the loop will execute even before the actual 
loop starts executing.E
Unlike while loop, in for loop we have 3 parts in the for header.E
E
Syntax:

for (init-statement; condition; final-expression) {E
 statementE
}


E
Init-Itatement: This statement is used to initialize or assign a starting value to a variable which may be altered 
over the course of the loop (we will see this while solving examples). It is used/referred only once at the start of 
the loop.E
E
Condition: This condition serves as a loop control statement. The loop block is executed until the condition 
evaluates to true.E
E
Final expreIIion: It is evaluated after each iteration of the loop. It is generally to update the values of the loop 
variables.E
E
Now that we know the use of each of these, let's understand it with an actual loop.E
E
Execution flow of for loop:


	 for (int index = 0; index != 5; indexÀ+) {

 System.out.print(index + “ “);

 _

E
Output - 0 1 2 3 4 

Herek
$A Init-statement is executed only once at the start of the loop. In this example, index variable is defined and 
initialized to 0. D
GA Next, the condition is evaluated. If index is not equal to 5, the for body is executed. Stherwise, the loop 
terminates. If the condition is false in the first iteration itself, then the for body is not executed at all.D
šA If the condition is true, the for body executes. In this case, the for body prints the value of index (the print 
statement). D
RA Finally, the final-expression is evaluated. In this example, index is incremented by %.
Cracking the Coding Interview in JAVA - Foundation
These four steps represent the first iteration of the for loop. Step 1 is executed only once on entry to the loop. 
Steps Ÿ, 3, and 4 are repeated until the condition evaluates as false i.e. index becomes equal to 5.


Acceptable alternatives in for loop: 



Omitting parts of for loop



In a ‘for’ loop, we can omit any (or all) of init-statement, condition and final-expression. 


1. We can omit the init-statement when an initialization is unnecessary. This may be the case when the 

 variable may have already been declared„
 Example-

 int index = 0;

 for(; index < 5; index+C)

 System.out.println(index);

 Note that the semicolon is necessary to indicate the absence of init-statement—more precisely, the 

 semicolon represents a null init-statement.


2. Omitting the condition is equivalent to setting it as true. Because of this, the for loop must have an exit 

 statement inside the loop. Otherwise, it may lead to a never-ending or infinite loop which is a nightmare for 

 any processing system.

 Example-

 for(int index = 0; ; index+C) 

 {

	 statement + code inside the loop must stop the iteration!

 }


3. We can also omit final expression. In such loops, either the condition or the body must do something to 

 advance the iteration, otherwise the loop will not run any further owing to lack of information„
 Example-

 for(int index = 0; index = 5; ) {

	 System.out.println(index);

	 index = index + 1;

 x


Note B
wƒ The above statements can all be omitted together too.
žƒ We can also have multiple statements inside the loop.

 Let us look at this example to know what we are talking about


 for(int i = 0, j = 14; i < 10 && j > 5; i+C, j––);

 Here, you may see that we are handling two variables, conditions wrt both and final expression, all in one for 

 loop.



 This is why it is the most popular loop of all.


Let us take the same previous example - 



Print the first 10 natural numbers. 
Cracking the Coding Interview in JAVA - Foundation
To a€€omplish this with a for loop-G
0 W_ d_€lar_ and d_fin_ th_ int variabl_ ‘i’ (int i=1), but this tim_ w_ do it as a part of for loop.G
& W_ put th_ €ondition as i to b_ l_ss than or _qual to 10. G
^ Insid_ th_ for loop body, w_ print th_ valu_ of ‘i’.G
h Finally in th_ final-_xpr_ssion, w_ in€r_m_nt th_ valu_ of th_ variabl_ ‘i’.


CodeH
for iint i = 1; i <= 10; i++) {

	System.out.printlnii + “ “);

1



Output - 1 2 3 4 5 6 7 8 9 10



'ry these using for loopH
1. Print th_ sum of th_ first 10 natural numb_rs.

2. Writ_ a short program that prints _a€h numb_r from 1 to 100 on a n_w lin_. 

 For _a€h multipl_ of 3, print "Fizz" inst_ad of th_ numb_r.

 For _a€h multipl_ of 5, print "Buzz" inst_ad of th_ numb_r. 

 For numb_rs whi€h ar_ multipl_s of both 3 and 5, print "FizzBuzz" inst_ad of th_ numb_r.