Which C string function is used to reverse a string?

Developed back in 1972 by Dennis Ritchie, C language is one of the oldest programming languages . To date, the procedural language is widely used and its concepts are vast to understand. 

While we consider C language’s concepts, reversing a string is pretty complex to comprehend.

To reverse a string in C programming language, there are various methods but each has its ultimate logic. 

In this article, we will keenly look at which string function is broadly used to reverse a string and what are the other possible methods one can employ. 

What is a string in C language?

A string is usually a series of values that are aligned and attached to a particular variable. For example: AUDACITY, is a string. String is one of the most explored data structure and algorithm concepts as many interview questions will come based on it. Many a time, questions like what is a string used for, explain longest common substring, how to reverse a string, etc, will all be asked. 

However the methodology of strings varies according to programming languages. Specifically, in the C programming language, strings have a deeper concept. In C, every sequence of values is ended with a \0 which is a null character. 

Moreover, strings are also considered as an array of characters. The only difference between a string and array is that, in an array there won’t be a termination with a null character as mentioned above.

Now let us particularly understand what reversing a string means before moving on to how it can be done. 

What does reversing a string mean?

Say you have created a particular string and you want to flip it. To do that, you’ll need to apply the reverse a string algorithm and it will make your software do it. For eg: TAYA is your string and when you apply the reversing algorithm it becomes AYAT. 

Interesting fact, there are multiple purposes of reversing a string. Sometimes the words can be understandable only if the string is reversed, so this methodology has been used by coders to convey secret messages as well!

Also, reversing a string has been used to figure whether a said palindrome string is true. Palindrome strings are unique as even if we reverse it, it’ll convey the same output. Example: RACECAR if reversed is RACECAR only. 

In the C language, there are multiple ways to reverse a string. Usually, it gets reversed with the strrev function but there are various methods through which the desired output can be obtained. 

Let us now look into the methods to reverse a string in C language. 

Methods to reverse a string in C programming language

With various approaches to reverse a string, below are the commonly and most popularly used approaches.

• Strrev function

• String with string

• Swapping

• Recursion

• Pointers

• Stack

Strrev function

Strrev function is the most popular technique when it comes to string reversing. Strrev is often found in the string.h list and it easily and directly processes a reversal of a string. As its code is inbuilt inside the library, we only need to input string values and not actually type out a code.

Using a string

The next way to reverse a string is by using a string itself. It simply is done to transfer the values of one string to another but in the reversed order. For this method to work, we only need the string’s size as it will start copying one string’s character to the next string in a reverse way. 

Swapping method

Swapping is the best method to save space while reversing a string. For this method, you will need two pointers, one at the start and another in the end. This method will swap all the characters of the string from the first pointer to the second. Through this technique, an in-place reversed array gets formed. 

Recursion

Recursion is one of the well-known coding methods which breaks down a tough problem into tiny ones, so the solution can be quickly found. Moreover, in recursion, a function calls itself until the result is produced. To reverse a string, the one value from the input string must be taken away. Then the recursive function must be called. Once it gets called, the removed value must be applied again so that the reverse option saves it. 

Pointers

Previously we saw how in the swapping method, the characters get transferred from the start pointer to the end. In the pointer method, the pointers themselves will be reversed. For example, say, the start pointer is A and the end is B. It will turn into B as the first pointer and A as the last pointer. 

Stack

In data structure concepts, stack is the most simplest one and they’re best used for reversing. As stack’s algorithm practices LIFO (Last in First out), the reversing of a string is straightforwardly done. The basic idea is that all the elements of the string will first get inside the stack, and one by one in a reverse order it will pop out and form a string. 

For eg: In the string HELLO, the letter O goes lastly into the stack. As the last goes in, it comes out first. So it’ll be OLLEH. 

Note: Be it whatever method, strrev () is the most used c string function to reverse a string. It doesn’t require any coding as it already is inbuilt. It easily flips a string and gives the desired output. But the other methods are also vital for certain rare problems that cannot be delivered with only strrev ().

Conclusion

Practicing array or string based problems can be super beneficial for tests and interviews. We hope through our blog you’ll be able to answer how to reverse a string in C language when an interviewer asks you it. With the help of these approaches, one can reverse even a longest common substring or subsequence, easily.