Difference Between for and while loop

In C++ and Java, the iteration statements, for loop, while loop and do-while loop, allow the set of instructions to be repeatedly executed, till the condition is true and terminates as soon as the condition becomes false. Conditions in iteration statements may be predefined as in for loop or open-ended as in while loop.

There are several ‘for’ loop variations in C++ are implied to increase its applicability, power and flexibility. For example, the for loop allows us to use more than one variable inside the loop in order to control it, and the use of converge function with ‘for’ loop. Conversely, with while loop we can not use many variations, that must be used with the standard syntax.

There are some major differences between for and while loops, which are explained further with the help of a comparison chart.

Content: for Loop Vs while Loop

1. Comparison Chart
2. Definition
3. Key Differences
4. Conclusion

Comparison Chart

Basis for Comparison	for	while
Declaration	for(initialization; condition; iteration){ //body of 'for' loop }	while ( condition) { statements; //body of loop }
Format	Initialization, condition checking, iteration statement are written at the top of the loop.	Only initialization and condition checking is done at the top of the loop.
Use	The 'for' loop used only when we already knew the number of iterations.	The 'while' loop used only when the number of iteration are not exactly known.
Condition	If the condition is not put up in 'for' loop, then loop iterates infinite times.	If the condition is not put up in 'while' loop, it provides compilation error.
Initialization	In 'for' loop the initialization once done is never repeated.	In while loop if initialization is done during condition checking, then initialization is done each time the loop iterate.
Iteration statement	In 'for' loop iteration statement is written at top, hence, executes only after all statements in loop are executed.	In 'while' loop, the iteration statement can be written anywhere in the loop.

Definition of for loop

In Java, there are two forms of for loops. The first form is “traditional” form and the second is “for-each” form.

Syntax

The general form of traditional for loop statement.

for (initialization; condition; iteration)
{
//body of for loop
}

• Initialization: The initialization of the loop controlling variable of for loop is executed only once, during the first iteration of the loop. Here, the loop controlling variable is initialized, sometimes if the loop variable is not used again anywhere in the program and is only used as the controlling variable of the loop, then it is both declared and initialized in the ‘for’ loop.
• Condition: The condition of the ‘for’ loop is executed each time the loop is iterated.
• Increment and iteration: The iteration statement is an expression that increment or decrements the loop controlling variable.

Whenever the loop is executed, its initialization condition is executed first; then the condition is checked. If the condition is satisfied, the body of the loop is executed, then the iteration statement is executed. Then again, the condition is checked to know whether the loop will iterate further or will terminate.

In Java, the initialization statement and the iteration statement may include more than one statement. Each statement is separated by other by a comma, in Java, a comma is a separator whereas, in C++, “comma” is an operator that can be used in any valid expression.

for-each loop and its syntax

The “for-each” form is an enhanced for loop. The general form of the for-each loop is as follow.

for(type iter_variable: collection) statement-block

Here, the “type” specifies the type of iteration variable, followed by the iteration variable. The iteration variable will receive the element from the collection variable. The type must be the same as the type of elements stored in the collection variable. The for-each form of for loop automates the iteration of the loop from starting to end accessing the values in sequential order.

Example

There are various types of collection used with for loop. Let’s discuss it with an array as a collection.

public class Main
{ 
public static void main(String[] args) 
{ 
int array[]={10, 20, 30, 40, 50, 60}; 
int add=0; 
for( int c: array) 
{ 
System.out.println( "value in c " + c); 
add = add+c; 
} 
System.out.println("additon of array elements is " +add); 
}
}
// output
value in c 10
value in c 20
value in c 30
value in c 40
value in c 50
value in c 60
additon of array elements is 210

Here, ‘c’ is an iteration variable; it receives the values from array[ ], one at a time, from the lowest index to the highest index in the array. Here, the loop iterates until all the elements of the array are examined. It is possible to terminate the loop in between by using “break”. However, the change in the iteration variable does not affect the array, as it is only a read-only variable.

Definition of while loop

The while loop is the most fundamental loop available in C++ and Java. The working of a while loop is similar in both C++ and Java.

Syntax

The declaration of a while loop is as follows

while ( condition) 
{
statements; //body of loop
}

The while loop initially checks the condition and then executes the statements till the condition in while loop turns out to be true. The condition in while loop can be any boolean expression. When an expression returns any non-zero value, then the condition is true, and if the expression returns a zero value, the condition becomes false.

If the condition becomes true, then loop iterates itself, and if the condition becomes false, then the control passes to the next line of the code immediately followed by the loop. The statements or the body loop can either be an empty statement or a single statement or a block of statements.

Example

Let’s discuss the working of a while loop. In the example below the code will print from 1 to 10.

//example is in Java.
public class Main
{ 
public static void main (String args[]) 
{ 
int n=0; 
while(n<10) 
{ 
n++; 
System.out.println("n=" +n); 
} 
}
}
//output
n=1
n=2
n=3
n=4
n=5
n=6
n=7
n=8
n=9
n=10

Here, the initial value of ‘n’ is 0, which makes the condition in while loop true. The control then enters the body of the while loop and the value of ‘n’ is incremented according to the first statement in the body of a while loop.

The value of ‘n’ is printed, then the control goes back to the condition in a while loop, now the value of ‘n’ is 1 which again satisfies the condition, and the body of the loop is executed again. This continues till the condition is true, as soon as the condition becomes false, the loop is terminated.

Like ‘for’ loop, the ‘while’ loop can also initialize the control variable at the top of the loop i.e. during condition checking.

//for example
while((ch = getchar( ) ) != 'A')
{
System.out.println(" The input alphabet " +ch);
}

Here the control variable ‘ch’ is initialized, and the condition of the loop is verified at the top of the loop.

Note

May it be a for loop or a while loop, if there is only one statement in the body of the loop, the curly braces are not required in that condition.

Conclusion

The for loop and while loop both are iteration statement, but both have their distinct feature. The for loop do have all its declaration (initialization, condition, iteration) at the top of the body of the loop. Adversely, in while loop only initialization and condition is at the top of the body of loop and iteration may be written anywhere in the body of the loop.