implement Transposition cipher encryption and decryption technique

#include<stdio.h>
#include<conio.h>
#include<string.h>

char mssg[100],a[50],b[50],dmssg[100];
 
void get_mssg()
{
   printf("\n Enter the Plaintext : ");
   gets(mssg);
}

void en_mssg()
{
  int i=0,k=0,j;
 
  if(strlen(mssg)%2 == 0)
    j = strlen(mssg)/2;
  else
    j = strlen(mssg)/2+1;   
   
  while(i<strlen(mssg))
  {
   dmssg[k++] = mssg[i++];     

   if(mssg[i] == '\0')
    dmssg[j++] = '\0';        
   else
    dmssg[j++] = mssg[i++];  
  }  
  dmssg[i] = '\0';   
 
  printf("\n The Ciphertext is : ");
  puts(dmssg);
}

void de_mssg()
{
  int i=0,j,k=-1;
 
  if(strlen(dmssg)%2 == 0)
    j = strlen(dmssg)/2;
  else
    j = strlen(dmssg)/2+1; 
 
  int l = j;
  while(i < l && j < strlen(dmssg))
  {
    mssg[++k] = dmssg[i];   ++i;   mssg[++k] = dmssg[j];    ++j;         
  } 

  if(i<l)
   mssg[++k] = dmssg[i];
 
  printf("\n The Decrypted Plaintext is : ");
  puts(mssg);
}

int main()
{
  get_mssg();  en_mssg();  de_mssg(); 
  return 0; 
}