Question

The function below returns a substring of input string.

What is the invariant of this function?

Static string substring( String in, int ind) {

String t = in ;

t = t.substring(ind);

return t;

}

Answer 1

Answer:

Static string substring( String in, int ind) {
String t = in ;
t = t.substring(ind);
return t;
}

Here t.substring(ind) will return the string t from begin_index = ind to last_index = in.lenght() , in.length() will return the length of a string.
So here the invariant is the value of ind is greater than or eqaul to 0 and less than len(string).Because the String index starts from 0 and ends at length_of_string - 1.
So ind value must be between the above range other than that values it will raise an error(Index out of bound).

Invariant : 0 <= ind < in.lenght()

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