How to read an array without knowing its size in c. The dimensions of the matrix are known.

How to read an array without knowing its size in c As far as I understand, the way to do it is by allocating some memory for the array input by the user, and then reallocating it or freeing as needed. length] is incorrect because it initialises the array with the size of the input array, but I cannot get it to work otherwise. You should really specify which language you're using, though, and what you're trying to acheive, because the answers will vary depending on those things. There is no specified limit for the number of values inserted and I can't just declare an array of any size so is there a way to dynamically increase the size of the array to be able to hold more int values as they are Oct 2, 2019 · I want user input of the form {{a,b},{c,d}}, one single line, to represent a matrix. You can get its length from sizeof tricks, but you should never need to do that. name). The following code demonstrate usage: Dec 14, 2015 · Like the title says I'm trying to read an unknown number of integers from a file and place them in a 2d array. Is there anyway that let us enter the sentence without specified the size ?Hence we could enter the sentence without the limitation of 100,is it related to the pointer ? May 19, 2022 · How do you get the last element of an array without knowing its index? We will explore 3 simple ways with explanations of how they work. I've chosen to read input a character at a time Mar 4, 2014 · I want to read values (float) into an array but I don't know number of values. Jul 3, 2022 · Strings in the C programming language are very integral parts. In this article, we covered different ways to find the size of an array without using the sizeof operator. So I used scanf. Finding the end can be done in a few ways, you need to be given: the ending address explicitly the length of the array a sentinel value used to mark the end of the sequence In your first attempt, printArray(int* arr, int size) is This approach allows you to input an array without specifying its size in advance. Note that the above approach holds true only when Jul 23, 2025 · In many situations, we might want to take list as input without knowing the size in Python beforehand. Any help??? In Java, you cannot declare an array without specifying its size at the time of creation. In Java, you typically need to declare the size of an array when initializing it. Using getchar(), I cannot treat cases where the integers are larger than However, before you actually initialize an array you need to know how many elements are going to be in that array, normally by reading user input. So, when a beginner starts coding he may have a good understanding of the concepts of array and strings. Apr 25, 2021 · I have a pointer to an array in c to which I would like to iterate through but I don't know the size: You are in luck if you truly have a pointer to an array as the type of a pointer to an array carries information about the array size. First determine the total size of the array in bytes and divide it by the size of one element to get the number of elements. C++ Program to Take User Input in an Array The following C++ program uses a for loop and cin to take input from the user and insert it in the array. Aug 5, 2022 · @Leonardo Lovera "Read arbitrary length strings" --> How far do you want to take this? to read strings whose length meet/exceed INT_MAX, SIZE_MAX, UINTMAX_MAX or what? 2D array arguments need a size for all but the first dimension. Apr 11, 2010 · In this case, my array's size is not known beforehand. Explore simple methods to enhance your coding skills. Sep 4, 2020 · This method allocates a new array with the specified size, copies elements from the old array to the new one, and then replaces the old array with the new one. Apr 29, 2018 · Do you know if the cases when you can declare an array without a size specifier for the leftmost dimension are the same in C++ (obviously " struct " would probably need to be changed to " struct or class " )? I tried the function parameter case; it seems like the syntax is valid but the variable becomes a pointer (according to typeid(the_variable). Keep in mind that if you need a primitive array (e. Master the art of dynamic programming as you learn how to take array input in C++ without size. Obviously its size must be dynamic, so I guess my question is: Is there a way to declare the array without assigning its size, since I can just change it in the inspector window anyways? Aug 20, 2024 · Flexible Array Member (FAM) is a feature introduced in the C99 standard of the C programming language. Dec 4, 2020 · If you read from a file, you can afford to read the file twice: the first time, you do not store the values, you just count how many values there are; the second time, you allocate an array with the right size with malloc () and you store the integers into the array. How to do it if we are not allowed to use if-else, switch-case, and conditional statements? The idea is to use the fact that 'cin >> input' is false if the non-numeric value is given. But unfortunately it simply doesnt work. These methods are helpful when working with dynamic arrays or passing arrays to functions. This tutorial delves into the intricacies of compiling arrays without explicit size declarations, exploring innovative techniques that enhance memory efficiency and code flexibility in modern C++ development. Such an array inside the structure should preferably be declared as the last member of the structure and its size is variable (can be Jul 23, 2025 · In the first case, you are creating an array containing some element by implicitly declaring its size. Jul 23, 2025 · But instead of accessing a single element to take input in an array, we use a loop to iterate over the array elements and take input from the user for each element. If you don't know the size until run time, or the function has to take different sized 2D arrays, you can use a pointer to a pointer instead. Feb 10, 2019 · Is it possible to declare an array without assigning the size of an array? You can declare an array without a size specifier for the leftmost dimension in multiples cases: as a global variable with extern class storage (the array is defined elsewhere), as a function parameter: int main (int argc, char *argv []) . An array by definition is a fixed size throughout its lifetime, so you can't change it as you go. This is known as dereferencing the pointer. scanf will return -1 if there is nothing to scanf . However, you can declare an array variable and initialize it later with a size or use alternative data structures that can dynamically change size. Also in this program stack smashing is hapenning, which is a kind of buffer overflow, which in case program is trying to write data beyond the allocated limit. Jul 1, 2021 · C is willing to automatically size, allocate, and initialize arrays for you. I don't know how well you know C pointers, but array access in C (like array[2]) is actually a shorthand for accessing memory via a pointer. Both Arrays and Strings are widely used topics. This approach provides flexibility by allowing users to input as many elements as they want until a specified condition (like pressing Enter) is met. As we know that if we have to read an array or string of known length we have to use loops for it. Oct 20, 2024 · Discover powerful techniques to determine array size in C++ without sizeof (). Jun 23, 2022 · Consider a problem where we need to take an unknown number of integer inputs. I want to read in a file line by line, without knowing the line length before. But depending on what you are trying to do, a non-const pointer to const data may provide you with what you're going for. For example if the values introduced are 1, 2, 3, 0 then the array X will contain 1, 2 and 3 and the array size will be 3. For ex Jun 24, 2010 · The thing that's getting me is inside the inspector window, I am able to change the size of the array. The array does not contain the information about its size but we can extract the size using sizeof () operator. Oct 20, 2023 · I was trying to get array elements at run time without knowing it's array size. For the structures in C programming language from C99 standard onwards, we can declare an array without a dimension and whose size is flexible in nature. To access the memory pointed to by data, you write *data. getline (sentence,SIZE); cout <<sentence; getch (); return 0; } This is the simple coding that let us enter a sentence in a 100 element size of array variable. Introduction In the realm of C++ programming, understanding how to work with arrays without predefined sizes is a crucial skill for advanced developers. Jun 26, 2015 · The standard way to do this is to use malloc to allocate an array of some size, and start reading into it, and if you run out of array before you run out of characters (that is, if you don't reach EOF before filling up the array), pick a bigger size for the array and use realloc to make it bigger. g. With one exception, however, there is no way to automatically initialize a pointer that points to some other array. When in array the attained memory for the linked list can be freed. k. Nov 5, 2016 · The most important is that if you don't know the number of values you need to use a container that can grow as needed. I don't know what is mistake in my logic. Dec 3, 2013 · An array is simply a series of contiguous memory locations. a the user enters some numbers as arguments, and the program creates an array with that many arguments. With I prefer doing on a Linux kernel is to mmap as much space as required and then just use it. The final element when attained do the second suggestion and copy all the elements from the linked list into the array. The most common way of finding the size of an array involves using the sizeof operator, which returns the number of bytes used by a container or a variable. Here's what I got so far: Feb 19, 2009 · cin. This guide will explore how you can achieve that using array literals and alternative data structures such as ArrayLists. In order to dynamically set the size of the array, you need to use the malloc () or calloc () functions. , int []), you would need to convert the ArrayList to a primitive array after reading the elements. Note that a 2D array type is not directly convertible to a pointer to a pointer, so Array : How to read float input without knowing size in java?To Access My Live Chat Page, On Google, Search for "hows tech developer connect"As promised, I h. Nov 28, 2016 · I've been reading about how to declare an array when we don't know its size beforehand. However, you can create an array without explicitly providing its size in different ways. Arrays do not grow as you use them, you must preallocate, same for pointers. Feb 27, 2015 · So if as you say the array has unknown size then the compiler can not calculate the size of the memory occupied by the array. Dec 13, 2018 · How to input a large number (a number that cannot be stored even in long long int) without spaces? We need this large number in an integer array such that every array element stores a single digit. Aug 3, 2016 · How to write in an array without size! I wanna have a program which read's an unknown numbers of data from user and then sum them up!!! Thanks Is there a way of copying a string into a new string without knowing the size that the new array has to be at compile time? As far as I am aware, you can't have variable array lengths in C. Jun 22, 2018 · There is no such thing as an "array of unknown size". Oct 17, 2025 · The Length of an array in C refers to the maximum number of elements that an array can hold. It must be specified at the time of declaration. I've found multiple questions that are similar, like this one. variable size character arrays. I am trying to read some text file into a 2D array, but I was wondering how this would be possible without knowing the size of the array (only the maximum size it can be). Feb 25, 2011 · The size of that array depends on what the user types. array must be a one-dimensional array. Apr 24, 2015 · Like in title, can I somehow get size of dynamic allocated array (I can't keep it separately), or somehow loop through this array without using it's size? Jun 19, 2017 · It should not be possible to not know its length. Then the calling code can either allocate memory to a pointer to a pointer or convert the array somehow. It could be "John" or "because", i. Jun 1, 2013 · 12 There is a new function in C standard for getting a line without specifying its size. Here's how the read-and-allocate loop might look. How to read in lines of a file in C without knowing the size Hello I am trying to read in a file line by line into a char * and fgets needs a size but I don't know the size of the line. So I want to pass the array as a parameter to a function without specifying it's size explicitly in my code. getline function allocates string with required size automatically so there is no need to guess about string's size. Oct 17, 2025 · The size of the array refers to the number of elements that can be stored in the array. Here, the compiler is able to determine the number of elements inserted and automatically creates an array of that size. At your level, the normal way to do this would be to declare a sufficiently large array (but check those limits). I am really stuck with this. In C, we don't have any pre-defined function to find the length of the array instead, you must calculate the length manually using Jul 23, 2025 · The simplest method to find the size of an array in C is by using sizeof operator. The array's contents are intended to be used for mathematical calculations, but the number of values stored inside the array depend upon user input. Apr 17, 2023 · Declaration of an array without specified size in not valid in C language, as here compiler may be allocating an array of default size. Since data is of type int *, then *data is of type int. Mar 7, 2017 · I've got a question about creating an array in C# when I don't know the exact number of elements. e. Second thing is I want to store this values in an array. A typical solution is to run a loop and stop when a user enters a particular value. Mar 21, 2021 · I am aware that int[] res = new int[input. And this is leading to the undefined behaviour of this program. Arrays in C don’t have built-in methods for accessing their size. It is also known as the size of an array that is used to determine the memory required to store all of its elements. Arrays are generally a fixed size, so that might be tricky. Once you have your number of elements, you can then either choose to allocate an array on the heap or stack. In the second case, you haven't specified the array size, but you have inserted its values. An array without an initial size is basically just a pointer. If its an array, you allocated it with type arr [size]; and if its a pointer, you allocated it with type *arr = new type (size); In both cases, you have size. #include &lt;iostream&gt; #include &lt;fstream&gt; using namespace std; int main() { Feb 7, 2015 · Is there a way to make an array in Java, without defining or asking for its length first? A. So it is evident that anArray is pointer to first element of the array that you might pass to the function. Say in first case {4,3,5,6,11,22} In second case {11,22,77,43,2,1,2111,322} Say i want to read 10 integer values from the user (second time 5 int value) (depends on each cases). Learn template functions, pointer arithmetic, and more in this comprehensive guide Aug 9, 2012 · 1 You have described an array of int, not a class that implements a InputIterator, which is what the for_each is designed for, even though you can use it to iterate an array, but you need to know the size of the array to iterate it. To read unknown number of elements, consider using std::vector. Now you may immediately say, why not just use a size 100 array and the user fills in whatever number under 100 and you simply add a '\0' termination. In order to traverse an array you need to know two things, the starting address and how to find the end. For that you have std::vector (as mention by others already). Mar 16, 2014 · You cannot initialize an array at compile-time if you are determining the size at run-time. The dimensions of the matrix are known. As said, vectors do what you May 29, 2015 · 1 I want to read n values from the user but i don't know the value of n. ophqj fpbz osmmj qguqm cspovh tid qhit cog ahzqoblpz cvvoovdz cuqd ncxl kif uvacyz ryprz