Turbo C : Roman letter to number

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

void main()
{

         clrscr();
         int *a,l,i,j,k;
         char *s;

         printf("Enter The Roman Number");
         scanf("%s",s);

         l=strlen(s);

         for(i=0;i<l;i++){

         if(s[i]=='I')
                  a[i]=1;
         else if(s[i]=='V')
                  a[i]=5;
         else if(s[i]=='X')
                  a[i]=10;
         else if(s[i]=='L')
                  a[i]=50;
         else if(s[i]=='C')
                  a[i]=100;
         else if(s[i]=='D')
                  a[i]=500;
         else if(s[i]=='M')
                  a[i]=1000;
         else
                  {
                  printf("Wrong Input");
                  getch();
                  exit(0);
                  }
         }

k=a[l-1];
for(i=l-1;i>0;i--){
         if(a[i]>a[i-1])
                  k=k-a[i-1];
         else if(a[i]==a[i-1] || a[i]<a[i-1])
                  k=k+a[i-1];
}

printf("%d",k);

getch();
}