Octal to Hexadecimal in C

#include <stdio.h>  
#include<string.h>  
int main()  
{  
  int octaltobinary[]={0,1,10,11,100,101,110,111};  
  char hexadecimal[10];  
   char hex[10];  
  long int binary=0;  
  int octal;  
  int rem=0;  
  int position=1;  
  int len=0;  
   int k=0;  
  printf("Enter a octal number");  
  scanf("%d",&octal);  
// Converting octal number into a binary number.    
while(octal!=0)  
  {  
      rem=octal%10;  
      binary=octaltobinary[rem]*position+binary;  
      octal=octal/10;  
      position=position*1000;  
  }  
  printf("The binary number is : %ld",binary);  
    
  // Converting binary number into a hexadecimal number.  
  while(binary > 0)  
    {  
        rem = binary % 10000;  
        switch(rem)  
        {  
            case 0:  
                strcat(hexadecimal, "0");  
                break;  
            case 1:  
                strcat(hexadecimal, "1");  
                break;  
            case 10:  
                strcat(hexadecimal, "2");  
                break;  
            case 11:  
                strcat(hexadecimal, "3");  
                break;  
            case 100:  
                strcat(hexadecimal, "4");  
                break;  
            case 101:  
                strcat(hexadecimal, "5");  
                break;  
            case 110:  
                strcat(hexadecimal, "6");  
                break;  
            case 111:  
                strcat(hexadecimal, "7");  
                break;  
            case 1000:  
                strcat(hexadecimal, "8");  
                break;  
            case 1001:  
                strcat(hexadecimal, "9");  
                break;  
            case 1010:  
                strcat(hexadecimal, "A");  
                break;  
            case 1011:  
                strcat(hexadecimal, "B");  
                break;  
            case 1100:  
                strcat(hexadecimal, "C");  
                break;  
            case 1101:  
                strcat(hexadecimal, "D");  
                break;  
            case 1110:  
                strcat(hexadecimal, "E");  
                break;  
            case 1111:  
                strcat(hexadecimal, "F");  
            break;  
        }  
len=len+1;  
        binary /= 10000;  
    }  
  for(int i=len-1;i>=0;i--)  
{  
    hex[k]=hexadecimal[i];  
    k++;  
}  
hex[len]='\0';  
printf("\nThe hexadecimal number is :");  
for(int i=0; hex[i]!='\0';i++)  
{  
    printf("%c",hex[i]);  
}  
  
    return 0;  
}