Number sequences length, element first and last indexes in array

Question

Im beginner in programming. My question is how to count number sequences in input array? For example:

input array = [0,0,1,1,1,1,1,1,0,1,0,1,1,1]
output integer = 3 (count one-sequences)

And how to calculate number sequences first and last indexes in input array? For example:

input array = [0,0,1,1,1,1,1,1,0,1,0,1,1,1]
output array = [3-8,10-10,12-14] (one first and last place in a sequence)

I tried to solve this problem in C with arrays. Thank you!

Answer 1

Your task is a good exercise to familiarize you with the 0-based array indexes used in C, iterating arrays, and adjusting the array indexes to 1-based when the output requires.

Taking the first two together, 0-based arrays in C, and iterating over the elements, you must first determine how many elements are in your array. This is something that gives new C programmers trouble. The reason being is for general arrays (as opposed to null-terminated strings), you must either know the number of elements in the array, or determine the number of elements within the scope where the array was declared .

What does that mean? It means, the only time you can use the sizeof operator to determine the size of an array is inside the same scope (ie inside the same block of code {...} where the array is declared. If the array is passed to a function, the parameter passing the array is converted (you may see it referred to as decays ) to a pointer. When that occurs, the sizeof operator simply returns the size of a pointer (generally 8-bytes on x86_64 and 4-bytes on x86), not the size of the array.

So now you know the first part of your task. (1) declare the array; and (2) save the size of the array to use in iterating over the elements. The first you can do with int array[] = {0,0,1,1,1,1,1,1,0,1,0,1,1,1}; and the second with sizeof array;

Your next job is to iterate over each element in the array and test whether it is '0' or '1' and respond appropriately. To iterate over each element in the array (as opposed to a string), you will typically use a for loop coupled with an index variable ( 'i' below) that will allow you to access each element of the array. You may have something similar to:

size_t i = 0;
...
for (i = 0; i< sizeof array; i++) {
    ...  /* elements accessed as array[i] */
}

(note: you are free to use int as the type for 'i' as well, but for your choice of type, you generally want to ask can 'i' ever be negative here? If not, a choice of a type that handles only positive number will help the compiler warn if you are misusing the variable later in your code)

To build the complete logic you will need to test for all changes from '0' to '1' you may have to use nested if ... else ... statements. (You may have to check if you are dealing with array[0] specifically as part of your test logic) You have 2 tasks here. (1) determine if the last element was '0' and the current element '1' , then update your sequence_count++; and (2) test if the current element is '1' , then store the adjusted index in a second array and update the count or index for the second array so you can keep track of where to store the next adjusted index value. I will let you work on the test logic and will help if you get stuck.

Finally, you need only print out your final sequence_count and then iterate over your second array (where you stored the adjusted index values for each time array was '1' .

This will get you started. Edit your question and add your current code when you get stuck and people can help further.