SPOJ Problem:Bishops

#include<cstdio>
#include<cstring>
char s[105];
int l,i,j,a[105];
int main(){
    while(scanf("%s",&s)!=EOF){
    l=strlen(s);
    memset(a,0,sizeof(a));
    if(l==1&&s[0]<‘3‘)printf("%s\n",s);
    else{
        for (i=0;i<l;i++)
            a[l-i]=s[i]-48;
        for (i=1;i<=l;i++){
            a[i]=a[i]*2+a[i-1]/10;
            a[i-1]%=10;
        }
        a[1]-=2;i=1;
        while(a[i]<0){a[i+1]--;a[i]+=10;i++;}
        for (i=l;i;i--)
            printf("%d",a[i]);
        printf("\n");
        }
    memset(s,0,sizeof(s));
    }    
}