C++ is a general-purpose, object-oriented programming language. It is also a popular programming language as the TIOBE index ranks it 4th, and in this article, you will learn about a very important concept, i.e., C++ For Loop.
What is C++ For Loop?
A for loop is a control flow statement that is used to execute a piece of code based on the validity of some conditions. It makes the code execute repeatedly.
The syntax of for loop is:
for ( Initial state ; Condition ; Updation )
Body of loop
Fig: C++ For Loop Example
In the example above, the aim was to print the first 10 natural numbers. The condition that was given is - i less than equal to 10, which means the numbers will keep getting printed one after the other until i reaches 10.
Below you can see the output of the code.
Fig: C++ For Loop Output
The Layout of a For Loop
A for loop has three parts. First is initialization or initial state, the second is the condition, and finally the updation. So let’s understand these three parts or expressions.
Initialization: Initialization or initial state initializes the starting value. In this part of the loop, you declare and initialize loop variables. It executes only once, during the starting of the for loop.
Condition: For every iteration of for loop, a condition is checked. If the condition is true, the loop will continue and the execution will jump to those statements that are after the loop body. Otherwise, the loop will end.
Updation: The updation step is used to update the loop variable. This step increments or decrements the loop counter.
As you have gathered a basic understanding of for loop, now it’s time to understand the working of for loop in C++.
Working of For loop
Fig: Flowchart of for loop
When the execution of the for loop begins, it will execute at first the initialization section first. All the variables that you want to initialize are done here. It will execute only once; for example, if you are initializing a variable with 0 or 1, you don't have to do it every time.
After the initialization, the next task is to validate the condition and check whether the condition evaluates to true or false. If the condition results in true, then the code inside the body section would be executed, leading to the updation section. But if the condition results in false, then the code inside the body section wouldn't be executed.
After the completion of the body's execution, you will be headed towards the updation part, where there is an increment or decrement of loop variables.
After fulfilling the updation section, now again the condition is validated. If it returns true, then the entire process repeats for the updated variable. Else, the for loop terminates.
Now you will learn about excluding the expressions in C++ for loop
Excluding Expressions in for loop
As this article has discussed the three parts or expressions of for loop earlier, you can also write the for loop without these expressions as well. For example :
for ( ; ; )
As you can see, there are no expressions in the for loop, so it will produce an infinite loop. However, it is not used much.
Here is another example in which you will not include initial expression and updation expression inside the loop statement.
Fig: Excluding expression of For loop
As you can see, you haven’t initialized and updated the looping variable. You are initializing "i" with 0 before the loop begins and incrementing the loop using the increment operator with "i" inside the loop body.
The output of the program is as shown below:
Fig: Output of For loop
Nested for Loops
Nested for loops are mostly used while dealing with a two-dimensional array. It can be defined as a loop that is defined inside the body of another for loop. The loop which is inside the outer loop must finish the number of repetitions before the outer loop can continue to its next repetition.
Fig: Nested For loop syntax
Fig: Nested For loop Example
As you can see, this demo has used two for loops, i.e., x and y. So, when x=0, every value of y is evaluated under the condition y < 3. If it evaluates to be true, then for that particular value of x, every value of y, i.e., 0, 1, and 2, is printed until the condition is false.
Similarly, the flow repeats for x equal to 1 and 2.
It shows the output of the above code below:
Fig: Nested for loop output
In this article, you learned one of the fundamental concepts of programming, i.e., for loop. You looked at how a for loop works and the different expressions of for loop with some examples. Want to learn more about loops in C++? Check out our next tutorial on C++ While loop.
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