What does string find function return if it didn't get the string

#1

i don’t understand what is meaning and significance of size_t and string::npos

#2

@Rajan_42 i dont understand why have you added size_t here as it has no bearing on the answer, and it is just another datatype like int or float, you can look it up if you want to know more about it.
if find function finds a substring inside a string, it returns the starting index of the substring, if it is not found, a numerical value is returned, which can be written like this string::npos
you can directly use this value for comparison.
eg: if(str.find(s) != str::npos) //this will execute if substring is found

#3

@Rajan_42
The datatype size_t is unsigned integral type. It represents the size of any object in bytes and returned by sizeof operator. It is used for array indexing and counting. It can never be negative.