# TCL script to find sum of n natural numbers using looping statements

In this article, we will discuss the overview of TCL script and will cover the TCL script to find the sum of n natural numbers using looping statements with the help of an example. Let’s discuss it one by one.

**Pre-requisite –**

You can go through this article to understand a few basics through this link. https://www.geeksforgeeks.org/basics-of-ns2-and-otcltcl-script/.

**Overview :**

We will understand the syntax of the **while** loop and **for** loop in Tool Command Language with a simple example. In this example, we will first use the while loop to find the sum of the first n natural numbers, and then we will see how to use for loop to accomplish the same. We will also compare the syntax with a familiar language to understand it better.

**While-loop implementation :**

We will discuss the implementation steps as follows.

**Step-1 :**

The first step is to read a number from the user after prompting to do so. To read the number we use gets, and we use puts to give a prompt.

puts "Enter a number" gets stdin b

**Step-2 :**

Our next step is to initialize the sum to 0 and the iteration variable, i to 0. After this, we can have the while loop implementation of the code.

set sum 0 set i 0 while {$i<=$b} { set sum [expr $sum+$i] incr i }

**Note –**

The syntax of the while loop must be exactly as shown above. If you neglect the spaces or type the opening curly brace in a new line, the result will be an error.

**Step-3 :**

The implementation of the while loop specified above would like the following in C programming as follows.

sum=0; i=0; while(i<=b) { sum=sum+i; i++; }

**Step-4 :**

Finally, the whole code and output are as follows.**Code –**

puts "Enter a number" gets stdin b set sum 0 set i 0 while {$i<=$b} { set sum [expr $sum+$i] incr i } puts "The sum of first $b natural numbers is $sum"

**Output :**

**For-loop implementation :**

We will discuss the implementation steps as follows.

**Step-1 :**

The first 2 lines of code are the same as in the while loop. So, let’s look at the for loop implementation part.

set sum 0 for {set i 1} {$i<=$b} {incr i} { set sum [expr $sum+$i] }

**Note – **

The syntax of for loop must be exactly as shown above. If you neglect the spaces or type the opening curly brace in a new line, the result will be an error.

**Step-2 :**

The implementation of the for loop specified above would like the following in C programming as follows.

sum=0; for(i=1;i<=n;i++) { sum=sum+i; }

**Step-3 :**

Finally, let’s view the entire code and its output as follows.**Code –**

puts "Enter a number" gets stdin b set sum 0 for {set i 1} {$i<=$b} {incr i} { set sum [expr $sum+$i] } puts "The sum of first $b natural numbers is $sum"

**Output :**