C# Noob with a question: Int assignment not working as expected

Question

I'm trying a simple comparison here, assignment doesn't work as i would like... here is the code,

int returnDateIndex(Paragraph para)
{
    long firstIndex = 0;
    for (int i = 0; i < para.Words.Count; i++)
    {
        if (para.Words[i].Text == "Second")
        {
            if (para.Words[i - 1].Text == "First")
            {                        
                firstIndex = para.Words[i].FirstSymbolPosition;
            }
        }
    }     
    return (int)firstIndex;
}

I ran my debugger (In VS) and when that assignment is called, the int on the right was equal to 50, but the int on the left stayed equal to 0. No idea what I'm missing.

This application is using the Abbyy FineReader 9.0 SDK and the documentation for FirstSymbolPosition says it returns a read-only Long

EDIT: the code has been stripped of all features to make it easier for viewers to see where the problem is. I would appreciate answers for the original questions and anything else with the code that is bugging you as a comment please.

Answer 1

One obvious error is that you're expecting to return the first case where your conditions match (hence the firstIndex variable name), but you're really returning the last point where they match. This is also bad because it means you keep looking after finding your match. Another is that if the very first word in a sentence is "Second", you'll try to reference a negative index, which is very bad. Try this instead:

int returnDateIndex(Paragraph para)
{
    for (int i = 1; i < para.Words.Count; i++) 
    {
        if (para.Words[i - 1].Text == "First" && para.Words[i].Text == "Second")                        
            return (int)para.Words[i].FirstSymbolPosition;
    }
    return 0; // this is what your original code would have returned in a "not found" scenario
}

This code fixes both errors, and also completely side-steps your assignment problem.

Answer 2

As an aside you should add break after your assignment of firstIndex otherwise it could get overwritten by another value if the conditions are met later on in the loop.

Answer 3

In addition to what ChrisF said, this is pretty dangerous:

if (para.Words[i - 1].Text == "First")

There's no check in there to make sure i is greater than or equal to 1, if i is equal to 0 then you will be indexing out of the array.