Small Steps III — Thinking with Programs

Handling the not-found case

Handle the case when a value is not found.

What you will learn

A search can succeed or fail. The program should distinguish and report both cases.

Try it

void small_main()
{
    Array<int> numbers = {7, 2, 9, 4, 5};
    int value = input_int("Find: ");
    int index = -1;

    for (int i = 0; i < numbers.length(); i = i + 1)
        if (numbers[i] == value)
        {
            index = i;
            break;
        }

    if (index == -1)
        print("Not found");
    else
        print("Found at ", index);
}

Entering 9 in the console produces Found at 2; entering 8 produces Not found.

Here, break ends only the search loop, and the following if prints the result. Distinguish this from return, which ends the whole function.

Exercise

Use a linear search to find and print the first position of the character 'a' in a String. Use -1 if absent.

void small_main()
{
    String text = "Small C++";
    int index = -1;

    // find the first 'a'.

    print(index);
}

Hint

String also supports length and [], so this is almost the same as searching an Array.

void small_main()
{
    String text = "Small C++";
    int index = -1;

    for (int i = 0; i < text.length(); i = i + 1)
        if (text[i] == 'a')
        {
            index = i;
            break;
        }

    print(index);
}