Swap two string in C using third variable

/*Swap two string using third string*/

//swap one by one character using while loop

#include<stdio.h>

int main()

{

  int i=0,j=0;

  char String1[20],String2[20],Temp[20];

  puts("Enter first string");//can use "printf" also

  gets( String1 );//for read the input from user

  puts("Enter second string");

  gets( String2 );

  printf("Before swaping the strings are\n");

  puts( String1);

  puts( String2);

     while( String1 [i]!='\0')//loop till null character

      {

        Temp[j++]= String1[i++];

      } 

Temp[j]='\0';

   i=0,j=0;

  while( String2 i]!='\0')

      {

        String1[j++]= String2[i++];

      }

  String1[j]='\0';

  i=0,j=0;

  while(Temp[i]!='\0')

      {

       String1[j++]=Temp[i++];

      }

   String2[j]='\0';

  printf("After swaping the strings are\n");

  puts(str1);

  puts(str2);

  return 0;

}//end of main