Message Encoding [Corrected]

#include <iostream>
#include <cstring>
using namespace std;
class string_t
{
    public:
        char a,b;
};


int main()
{
    char str_src[100],str_dest[150],string_temp[150],choice[7],str_org[100];
    string_t str_mat[9][9];
    int i,order,j,k,m,c,len;
    //fflush(stdin);
    //gets(choice);
    cin>>choice;
    if(strcmp(choice,"ENCODE")==0)
    {
            cin.ignore();
            cin.getline(str_src,100);

            len=strlen(str_src);
            strcpy(str_org,str_src);
            order=1;
            while(order*order<(len+1)/2)
                order+=2;

            for(i=len;i<order*order*2;i++)
                str_src[i]='/';
            str_src[i]=0;
            k=0;
            for(i=0;i<order;i++)
                for(j=0;j<order;j++)
                {
                    str_mat[i][j].a=str_src[k];
                    str_mat[i][j].b=str_src[k+1];
                    k+=2;
                }

          str_dest[0]=str_mat[order/2][order/2].a;
          str_dest[1]=str_mat[order/2][order/2].b;

          i=order/2;
          m;
          j=order/2;
          k=2;
          c=1;
          while(c<order)
          {
              for(m=1;m<=c;m++)
              {
                  j--;
                  str_dest[k]=str_mat[i][j].a;
                  str_dest[k+1]=str_mat[i][j].b;
                  k+=2;
              }
              for(m=1;m<=c;m++)
              {
                  i--;
                  str_dest[k]=str_mat[i][j].a;
                  str_dest[k+1]=str_mat[i][j].b;
                  k+=2;
              }
              c++;
              for(m=1;m<=c;m++)
              {
                  j++;
                  str_dest[k]=str_mat[i][j].a;
                  str_dest[k+1]=str_mat[i][j].b;
                  k+=2;
              }
              for(m=1;m<=c;m++)
              {
                  i++;
                  str_dest[k]=str_mat[i][j].a;
                  str_dest[k+1]=str_mat[i][j].b;
                  k+=2;
              }
              c++;
          }
          for(m=1;m<order;m++)
          {
            j--;
            str_dest[k]=str_mat[i][j].a;
            str_dest[k+1]=str_mat[i][j].b;
            k+=2;
          }
          str_dest[order*order*2]=0;
          cout<<"OUTPUT IS\n"<<str_org;
          cout<<endl<<str_dest;
    }
    else if(strcmp(choice,"DECODE")==0)
    {
        //fflush(stdin);
        cin.ignore();
        cin.getline(str_dest,150);
        strcpy(str_org,str_dest);
        len=strlen(str_dest);
        order=1;
        while((order*order)<len/2)
            order+=2;
        str_mat[order/2][order/2].a=str_dest[0];
        str_mat[order/2][order/2].b=str_dest[1];
        i=order/2;
          m;
          j=order/2;
          k=2;
          c=1;
          while(c<order)
          {
              for(m=1;m<=c;m++)
              {
                  j--;
                  str_mat[i][j].a=str_dest[k];
                  str_mat[i][j].b=str_dest[k+1];
                  k+=2;
              }
              for(m=1;m<=c;m++)
              {
                  i--;
                  str_mat[i][j].a=str_dest[k];
                  str_mat[i][j].b=str_dest[k+1];
                  k+=2;
              }
              c++;
              for(m=1;m<=c;m++)
              {
                  j++;
                  str_mat[i][j].a=str_dest[k];
                  str_mat[i][j].b=str_dest[k+1];
                  k+=2;
              }
              for(m=1;m<=c;m++)
              {
                  i++;
                  str_mat[i][j].a=str_dest[k];
                  str_mat[i][j].b=str_dest[k+1];
                  k+=2;
              }
              c++;
          }
          for(m=1;m<order;m++)
          {
            j--;
            str_mat[i][j].a=str_dest[k];
            str_mat[i][j].b=str_dest[k+1];
            k+=2;
          }
          k=0;
          for(i=0;i<order;i++)
                for(j=0;j<order;j++)
                {
                    if(str_mat[i][j].a!='/')
                    {
                        str_src[k]=str_mat[i][j].a;
                        k++;
                    }
                    if(str_mat[i][j].b!='/')
                    {
                            str_src[k]=str_mat[i][j].b;
                            k++;
                    }
                }
            str_src[k]=0;

          cout<<"OUTPUT IS"<<endl<<str_org;
          cout<<endl<<str_src;

    }



  return 0;

}