Permutation of String (#123)

* added Permutation of String

* permutation of string.c

the main object is to explain the code more easy

* permutation of string.c

the main object is to explain the code more easy

* updated readme

* done all the recommend changes.

* added link of Permutation of string

* Update and rename Permutation of String.c to Permutation-of-String.c

- rename according to the naming conventions 
- changed gets() to fgets()

* update index readme of strings

correctly linked [Permutation of String] after renaming of the file

Co-authored-by: Arsenic <54987647+Arsenic-ATG@users.noreply.github.com>

strings/README.md

@@ -8,6 +8,7 @@
 4. [Rabin Karp String Searching](c-or-cpp/rabin-karp.cpp)
 5. [String Tokeniser](c-or-cpp/string-tokeniser.cpp)
 6. [String Reversal](c-or-cpp/string-reverse.cpp)
+7. [Permutation of String](c-or-cpp/Permutation-of-String.c)
 
 ### C#
 

strings/c-or-cpp/Permutation-of-String.c

@@ -0,0 +1,65 @@
+// program to generate all permutation of the given string
+
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+
+//declare permutation and swap functions
+void permutation(char *,int,int);
+void swap(char *,char *);
+int main()
+{
+    char *s;
+    // dynamically creating string length
+    s=(char*)malloc(sizeof(char)*1000);
+    // getting string
+    fgets(s,1000,stdin);
+    // changing size to the length of string+1 to store null at end 
+    s=realloc(s,strlen(s)+1);
+	//calling permutation
+    permutation(s,0,strlen(s)-1);
+return 0;
+}
+void permutation(char *str,int s,int e)
+{   //declare variables
+    static int count;
+    int i;
+	//base condition
+    if(s==e)
+    {
+        count++;
+	    //Printing the string permutation's
+        printf("%d(%s)\n",count,str);
+    }
+    else
+    {
+        for(i=s;i<=e;i++)
+        {  //swapping variables value
+            swap(str+s,str+i);
+			//calling permutation function
+            permutation(str,s+1,e);
+			//now swap the variables value and make it before one
+            swap(str+s,str+i);
+        }
+    }
+}
+//swap function
+void swap(char *a,char *b)
+{
+    char temp;
+	//putting value in temp
+    temp=*a;
+	// putting value in a pointer
+    *a=*b;
+	//now putting value of temp in b pointer
+    *b=temp;
+	//swapping done
+}
+// Example:
+//Input: abc
+//Output: 1(abc)
+//        2(acb)
+//        3(bac)
+//        4(bca)
+//        5(cba)
+//        6(cab)