Added Article for Reverse a String in C

projects/reverse-a-string/_posts/2020-10-01-c.md

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+---
+title: Reverse a String in C
+layout: default
+last-modified: 2020-10-01
+featured-image:
+tags: [c, reverse-a-string]
+authors:
+  - abhishek_raut
+---
+
+In this article, we will see how to reverse a String in C!
+
+## How to Implement the Solution
+
+Below is the whole code for reversing a string in C :
+
+```c
+#include <stdio.h> 
+#include <string.h> 
+
+void reverseString(char* str) 
+{ 
+    int len, i; 
+    char *start, *end, temp;
+    len = strlen(str); 
+    start = str; 
+    end = str; 
+
+    for (i = 0; i < len - 1; i++) 
+    {
+        end++; 
+    }
+
+    while (start<end) 
+    { 
+        temp = *end; 
+        *end = *start; 
+        *start = temp; 
+
+        start++; 
+        end--; 
+    } 
+} 
+
+// Driver method 
+int main() 
+{   
+    // Change Input as needed
+    char str[400] = "AbCdeF"; 
+    printf("Input string: %s\n", str); 
+    reverseString(str); 
+    printf("Reversed string: %s\n", str);   
+    return 0; 
+} 
+```
+<br/>
+
+### Approach
+
+
+Here we create two pointers, one that points to the string's start and the other to the end of the string. Using a third character *variable* as a place holder, we swap the character positions indicated by the pointers. We continue to do so until the entire input string is reversed by moving the *pointers*. 
+
+[Time complexity][1]: O(n)
+
+<br/>
+
+### Breakdown
+
+Now let us see step-by-step how the code works.
+
+```c
+#include <stdio.h> 
+#include <string.h> 
+```
+Here we are including header files (.h files) to use functions like printf(). Header files provided us with tested ready to use functions to ease the software development work. 
+
+By including `#include <stdio.h>` we can use printf() method without worrying about how it is implemented. Can you guess why we have included `#include <string.h>`? Keep on reading for the answer.
+
+```c
+void reverseString(char* str) {
+    // code
+} 
+```
+This is the function that will take a string as input and reverse it. Here, we will be modifying the value pointed by *pointer* str. Hence, the function doesn't need to return anything, and the return type of our method is *void*. 
+
+```c
+    int len, i; 
+    char *start, *end, temp;
+    len = strlen(str); 
+    start = str; 
+    end = str; 
+```
+Here we are declaring *variables* to store the length of the string and *pointers* to point start and end points (of the logical substring) to be swapped. Note that currently, the `end` pointer is pointing to the start of the string instead of the end of the string. We will see how to fix it in the next step.
+
+And yes, the function `strlen()`, which gives us the length of string, can be used because of the statement: `#include <string.h>`. 
+
+```c
+     for (i = 0; i < len - 1; i++) 
+    {
+        end++; 
+    }
+```
+We traverse through the entire string so that *pointer* `end` can point to the last character of the string. It's important to note that *for loop* traverse till `len-1` this is because, in C, arrays are zero-indexed i.e., indexing starts from 0. The `++` syntax at the end of the *variable* `end` is called an Increment operator. The increment operator increments the value of the variable by one in each iteration. Thus, after *for loop* is executed, *variable* `end` points to the string's last character.
+
+```c
+  while (start<end) 
+    { 
+        temp = *end; 
+        *end = *start; 
+        *start = temp; 
+
+        start++; 
+        end--; 
+    } 
+```
+And this is the Meat of the matter; this is the logic that reverses the string. The *while loop*  condition `start<end` make sure that once reversed, we don't reverse back the string to the original string (For Math geeks; only 180° and not 360° rotation of string). The `temp` *variable* is used for swapping the characters pointed by two *pointers*. The `--` syntax at the end of the* variable* `end` is called a Decrement operator, and it decrements the value of `end` by 1. Both of these operators change characters pointed by the *pointers*, and we can swap all characters of the string. 
+
+```c
+ int main() 
+{   
+    // Change Input as needed
+    char str[400] = "AbCdeF"; 
+    printf("Input string: %s\n", str); 
+    reverseString(str); 
+    printf("Reversed string: %s\n", str);   
+    return 0; 
+} 
+```
+The `main()` function is acting as a utility function to use the `reverseString()`.  Using the instructions in the next step, try changing the value of *variable* `str` by typing your desired string inside double quotes *("")*.
+
+Also, think about how the length of the string being odd or even can affect our code.
+
+
+## How to Run Solution
+
+The easiest way to run this program is to go to this [LeetCode Playground][2] and run the program. You can tweak the program or provide different input strings to understand the working better.  
+
+Alternatively, you copy GitHub's code and run the program on an online C compiler or in an IDE.
+
+## Further Reading
+
+- [Reverse a String in C][3] on The Renegade Coder
+
+[1]: https://en.wikipedia.org/wiki/Time_complexity
+[2]: https://leetcode.com/playground/L5WCHB4x
+[3]: https://therenegadecoder.com