为啥错

#include<bits/stdc++.h>
using namespace std;
char a[25],b[25];
int main(){
    long long la,lb,j,s,i;
    cin>>a>>b;
    la=strlen(a);
    lb=strlen(b);
    if(la>lb){
        for(i=0;i<=la-lb;++i){
            s=0;
            for(j=0;j<lb;++j){
                if(a[i+j]==b[j]){
                    break;
                }
            }
            if(j==lb){
                cout<<b<<" is substring of "<<a;
            }else{
                cout<<"No substring";
            }
            return 0;
        }
    }
    if(lb>la){
        for(i=0;i<=lb-la;++i){
            s=0;
            for(j=0;j<la;++j){
                if(a[i+j]==b[j]){
                    break;
                }
            }
            if(j==la){
                cout<<a<<" is substring of "<<b;
            }else{
                cout<<"No substring";
            }
            return 0;
        }
    }
    if(la==lb){
        for(i=0;i<la;++i){
            if(a[i]==b[i]){
                ++s;
            }
        }
        if(s==la-1){
           cout<<a<<" is substring of "<<b;
           return 0;
        }
        cout<<"No substring";
        return 0;
    }
    return 0;
}