My code to find no. of a substrings in a string. Why is j<=str.length() - 3 causing runtime error?

Question

    #include <iostream>
    #include <string>
    using namespace std;
    
    int main() {
        
        int T;
        int count = 0;                                      
        cin>>T;
        
        for(int i = 0; i<T; i++) 
        {
            
            string str;
            cin>>str;
            count = 0;

---

• This part is for checking how many occurrences of "xyz" are there in my code.

• The test conditon j<=str.length() - 3 in for loop is causing error for some test case(s).

• When I run the for loop test condition j<=str.length() it does not give error.

   for(int j = 0;j<=str.length()-3; j++) { string x; x = str.substr(j, 3); if(x =="xyz") { count++; } } if(count) { cout<<count<<endl; } else { cout<<"-1"<<endl; } } return 0;

  }

Answer 1

String lengths use unsigned math; 2-3 becomes 2^64-1. Try j<-3 || j+3<=str.length() j<-3 || j+3<=str.length()