LA 5047 wrong answer

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

int main()
{
    char a[20], b[20];
    int n,i;
    scanf("%d",&n);
    for(i=1;i<=n;i++){
        scanf("%s %s",a,b);
        int lena,lenb,j,k=0,cnt=0,cn=0,num=0;
            lena=strlen(a);
            lenb=strlen(b);

            if(lena<lenb)
                printf("Case %d: Wrong password.\n",i);

            else if(lena==lenb){
                for(j=0;j<lena;j++){
                    if(a[j]==b[j])
                        cnt++;
                    if(((a[j]-64)==(b[j]-96))||((a[j]-96)==(b[j]-64)))
                       cn++;
                }
                if(cnt==lena)
                    printf("Case %d: Login successful.\n");

                else if(cn==lena)
                    printf("Case %d: Wrong password. Please, check your caps lock key.\n",i);

                else
                    printf("Case %d: Wrong password.\n",i);
            }
            else if(lena>lenb){
                for(j=0;j<lena;j++){
                    if((a[j]-48)>=0 && (a[j]-48)<=9){
                        num++;
                        cnt++;
                        cn++;
                        continue;
                    }
                    if(a[j]==b[k])
                        cnt++;

                    else if(((a[j]-64)==(b[k]-96))||((a[j]-96)==(b[k]-64)))
                        cn++;

                    k++;
                }
                if(num>0){
                    if(cn==lena)
                        printf("Case %d: Wrong password. Please, check your caps lock and num lock keys.\n",i);

                    else if(cnt==lena)
                        printf("Case %d: Wrong password. Please, check your num lock key.\n",i);

                    else
                        printf("Case %d: Wrong password.\n",i);
                }
                else
                    printf("Case %d: Wrong password.\n",i);
            }
        }
    return 0;
}