Reverse a string without using built in function

In interviews, the reverse a string question is frequently posed. However, interviewers often rephrase this inquiry, asking candidates about ‘Various Methods to Reverse a String‘ or ‘Reversing a string using a for loop.’ Your response would remain consistent.

In this specific post, we’ll discuss how to reverse a string without using built-in functions or how to reverse a string without a second array.

Understand Logic behind reverse a string

The logic is straightforward; we are utilising the C# language to handle this operation. However, other programming languages could also be employed.

A string is a collection of characters, which means we can convert a string to a character array or utilize a string as a character array to manipulate it. For further information on how strings operate, please refer to this official link.

We’re going to execute the same process as discussed earlier. We’ll utilize the string as a character array and employ a for loop to retrieve individual elements from the string. In other words, we’ll use a reverse loop to access the elements from the last to the first in the given string to accomplish this program.

Program to reverse a string in C#

First, brainstorm what you would do initially. If you are a regular visitor, you might construct a structure in your mind and commence with the necessary variables to accomplish this program. If you are not familiar, please refer to our ‘pyramid’ and ‘pattern’ posts where I detail how to approach any programming logic and devise your own strategy to tackle any problem.

Let’s delve into the code to solve this problem.

Step 1

The initial step is to declare the necessary variables. In our case, you can create two string variables named ‘myString’ and ‘output’. ‘myString’ represents the string provided by the interviewer, and ‘output’ is a string that displays the output.

TIP: Always create your variables according to their usage; otherwise, after some time, you may struggle to understand your logic.

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static void Main(string[] args)
{
    string myString = "moc.noitaraperpsweivretni";

    string output = "";
    
    Console.WriteLine(output);
}

Step 2

In the second and final step to complete this program, you’ll create a for loop. Your iteration will start with the string length – 1 because the length of the array is always one more than the collection. Then, add a condition where your iteration must be greater than or equal to 0, and finally, increase your iteration by 1 step.

static void Main(string[] args)
{
    string myString = "moc.noitaraperpsweivretni";

    string output = "";

    for (int i = myString.Length -1 ; i >= 0 ; i--)
    {
        output += myString[i];
    }

    Console.WriteLine(output);
}

Your code should resemble the above description. If it does not, please refer to the ‘Understand Logic behind reverse a string’ section to comprehend it.

TIP: Do not commence your program until you completely grasp the logic you are about to implement. Otherwise, you may encounter obstacles in your logic along the way.

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Summarizing the how to reverse a string without using built in funcation

In the initial step of solving the problem, it’s essential to define the required variables. This includes creating string variables like ‘myString’ and ‘output’, where ‘myString’ represents the input string provided by the interviewer, and ‘output’ holds the reversed string.

The final step involves implementing a for loop to iterate through the characters of the input string in reverse order. The loop starts from the length of the string minus one and continues until the index is greater than or equal to zero, incrementing by one each time. This loop effectively retrieves the characters from the last to the first in the string, thereby reversing it.

It’s crucial to thoroughly understand the logic behind reversing a string before attempting to write the program. Rushing into coding without a clear understanding of the logic can lead to complications and errors along the way.