custom-strlen

Module 2

Back to Class 2 Prep

Resource: Custom strlen

We've already seen the strlen function, which returns the length of a string, in other words, the number of characters inside the string.

int len = strlen("Hello");
// the value of len is now 5

How does strlen figure out the answer?

Well, we actually know enough about strings now that we can do it ourselves. Let's write our own "custom" version of the strlen function.

Let's name our function charCounter. It will take a string parameter as input, and it will return an int.

int charCounter(string theString)
{
    // TODO figure out how many chars are in theString
}

To figure out the length of the string, we can simply inspect each of its characters, one by one, keeping track of the total as we go along, until we've reached the end.

We'll represent the answer with a variable, counter, which we initialize to 0. And for each new character that we encounter, we simply increment counter by 1.

We know we've reached the end of the string when we find that special character, '\0', the nul-terminator, which is the last char in every string and exists solely to signify: "Hey, this right here is the end of the string."

int charCounter(string theString)
{
    int counter = 0;
    
    // until we see '\0', the nul terminator...
    while(theString[counter] != '\0')
    {
        // ... continue incrementing counter
        counter++;
    }
    
    return counter;
}

BTW, remember that counter++ is just a fancy way of incrementing counter by 1. These three statements are all equivalent:

• counter++;
• counter += 1;
• counter = counter + 1;

Take a look at customstrlen.c for a complete example program that implements this function, and invokes it from inside main, resulting in behavior like this:

$ ./customstrlen
Please enter a string: Don't be silly.
That string is 15 characters long!