Any task which is repeated more than one time is called a loop. Basically, loops can be divided into three types as while, do-while and for loop. There are so many programming languages like C, C++, JAVA, PYTHON, and many more where looping statements can be used for repetitive execution.
In the C programming language, three types of loops have been used for the execution of the programs.
- While loop: While loop is a pretest loop. It first tests a specified conditional expression and as long as the condition, expression is true, action taken. While loop also known as an entry control loop.
While (condition)
{
Statement;
}
- Do-while loop: Do-while loop more like a while loop & except that it tests the condition at the end of the loop body. Do-while loop also known as exit control loop.
Do
{
Statement;
}
While (condition);
- For loop: A for loop enables us to program n number of steps together in one line. In for loop, a loop variable is used to control the loop.
For (initialization ; condition ; increment / decrement)
{
Statement;
}
There are no additional loops in C++ for programming execution. It is totally like C language.
- While loops: These are also known as indefinite pre conditional loops. There is no guarantee ahead of time regarding how many times the loop will iterate.
While expression:
Statements
- For Loops: For loop is a python loop which repeats a group of statements a specified number of times. Boolean condition, initial values of the counting variable and incrementation of counting variable specifies the component of loop.
For < variable > in < range >:
Statement 1
Statement 2
……….
……….
Statement n
- Nested loops: Python programming allows use of a loop inside another loop. This is called nested loop.
For iterating _ var in sequence:
For iterating _ var in sequence:
Statements
Statements
All other loops are the same as other languages & in this language a loop named as for-each loop have been specified.
- For each-loop: For Each loop is another approach to navigate through the array or collection
for (data type variable: array | collection)
{
…………
…………
Statements
…………
…………
}
- While loop: While loop iterates through a block of code if a specified condition is true
While (condition)
{
…………
…………
Statements
…………
…………
}
- Do-while loop: Do-while loop will execute the code block once, before checking if the condition is true, then it will repeat the loop if the condition is true.
do
{
…………
…………
Statements
…………
…………
}
While (condition);
- For loop: for loop is a control flow statement that iterates a part of the programs multiple times.
for (initialization; condition; increment/decrement)
{
…………
…………
Statements
…………
…………
}
- For loop: This loop iterates over a collection of values.
For any _ Variable in Collection _ of _ Values
{
// code to be executed
}
- Repeat loop: A repeat loop executes a set of statements till a terminate statement is found.
Repeat
{
# commands
If (condition)
{
Break
}
}
- While loop: Executes a set of statements till a condition is true,
While (condition)
{
// code to be executed
}
- For loop: for loop is a repetition control structure that allows you to efficiently write a loop that needs to execute a specific number of times.
for index = values
…………
Statements
…………
End
Example:
for a = 10:20
fprintf('value of a: %dn', a);
End
- While loop: The while loop repeatedly executes statements while a specified condition is true.
while expression
statements
end
Example: n = 10;
f = n;
while n > 1
n = n – 1;
n = f * n;
end
disp ([‘n! = ‘num2str (f)])
Output: 3628800
- Nested loops: Uses one loop inside another loop.
for m = 1:j
for n = 1:k
<statements>
end
- Nested while loop: While statement inside another while statement.
While < expression1>
While < expression2 >
< Statements >
end
end
- For the next loop: Allow us to go through a block of code for the specified number of times. Counter or any variable can be used to run the loop.
For Counter = Start To End [Step Value]
[Code Block to Execute]
Next [counter]
- Do while loop: Allow us to check for a condition and run the loop while the condition is met.
Do [while condition]
[Code block to execute]
Loop
Or we can write it as:
Do
[Code block to execute]
Loop [while condition]
- For each loop: Helps to go through each of the objects in a collection and perform some action on it. Also referred to as a for-each-next loop.
For each element in collection
[Code block to execute]
Next [element]
- Do until loop: It loops until the specified condition is met.
Do [ until condition]
[Code block to execute]
Loop
Or we can write it as:
Do
[ Code block to execute]
Loop [until condition]
The various loops in most common programming languages are
| Types | Explanation |
| for | It iterates a portion of the program multiple times. |
| while | It iterates a portion of the program repetitively until the condition is true. |
| do while | It iterates a portion of the programs once and then iterates according to the boolean condition. |
| Nested | It is a loop that iterates within another loop. |
| Nested while | While statement inside another while statement. |
| For each | Helps to go through each of the objects in a collection and perform some action on it. |
| Repeat | It iterates a block of code repetitively until break statement is found. |
| For Next | It iterates a portion of code for a specified number of times. |
| Do Until | It loops until specific condition has happened. |
- Syntax should be used as mentioned.
- Do not misplace a semicolon.
- Usage of comparison operators should be correct for example ‘<’ operator returns numbers lesser than the given number and ‘<=’ operator returns both the given number and the number lesser than that. This error is known as an off-by-one error.
- Usage of wrong conditional expression as the loop iterates as the condition is true and the loop will not iterate if the condition is false.
- While using the loop for iterating arrays use the correct initializing value because the array element starts from 0.
- Always initialize conditional value.
- Do not use the wrong condition as it will stop the loop to execute.
This topic is significant in the professional exams for both undergraduate and graduate courses, especially for
- B.Tech. / B.E. in Computer Science
- M.Tech. / M.E. in Computer Science
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