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2D Array Input in same line

How I take 2D array input in same line. in C# Console.ReadLine() allow us to take input one at a time .I want to take input as a row
int [,] arr = new int[m,n];
for(i = 0; i < m; i++)
{
for(j = 0; j < n; j++)
{
arr[i, j] = int.Parse(Console.ReadLine());
}
}
I want to take input this way
2 2,
10 20,
30 40

Entering a two-dimensional array on the command line is going to be error prone and frustrating for users. But if you MUST do it:
Figure out what symbols will separate values. (Commas, spaces?)
Figure out what symbols will separate array dimensions. (Pipes, perhaps? Whatever you choose, make sure it isn't the same symbol you use for separating values.)
Prompt the user for data and capture it into a string.
Validate the data.
Write a parser that parses your data into a multi-dimensional array.
I'd advise against trying to do this. But I don't dictate your requirements.

var delimiter = ' ';
for(var i = 0; i<n; i++) {
var row = Console.ReadLine();
var _arr = row.Trim().Split(delimiter);
for(var j=0; j<m; j++) {
arr[j, i] = int.Parse(_arr[j].Trim());
}
}
Update:
#mike-hofer, wholeheartedly agree with the "error prone and frustrating for users" characteristics of such way of input. I assume this is rather for a quick and dirty testing. Plus, exactly the same approach will be applied if you have to read the array from a file line by line, so there is some broader value in this question.
#rahi-ratul75, the code above does not do any error checking. The most likely error will be an entry which won't parse as an integer. You may want, therefore, to use int.TryParse(,) and, when false, ask to re-enter the line. The main logic, however, is there:
read the line
split it into an array
parse the entry into an integer

Range in for loop using Array

I'm pretty new to C# and want the users to be able to write in 5 numbers between 1 to 25. The issue I'm having is that I don't want the user to type a number over 25 or a number below 1.
Also this is a task for my studies and my teacher want us to use arrays so I'm not allowed to use List.
int[] usernum = new int[4];
for (int i = 0; i < usernum.Length; i++)
{
usernum[i] = Convert.ToInt32(Console.ReadLine());
}

Ok, to start off, some annotations to your code:
int[] usernum = new int[4]; // should be: new int[5];
for (int i = 0; i < usernum.Length; i++)
{
usernum[i] = Convert.ToInt32(Console.ReadLine()); // use int.TryParse instead
}
Now, I don't want to just give you the code, since this should obviously be a learning experience.
What you need to do, though is integrate a "validation" cycle. That means:
Read in string from user
Try to parse string to number
If that fails: back to 1.
Check if number < 1 or > 25
If so: back to 1.
If you are here, you passed both checks and can
set usernum[i] = number
Next "i"
Obviously, there are some slight variations in how you twist and turn your checks and arrange loops which are equally valid.
For example: You can decide if you want to check if number is inside bounds or if you want to check if the number is outside bounds and jump or not jump accordingly ...
Why int.TryParse instead of Convert.ToInt32?
There are some rule of thumbs that can spare you from severe headaches:
"Never trust user input"
"Do not use exceptions for control flow"
Using Convert here, breaks both.
For one, Convert.ToInt32 throws if the string does not represent an integer value (chars other than +-0..9, value > int.Max or < int.Min). So in using it, you trust the user to type in a valid integer. Not a good idea.
Then, it throwing means: the case, that a user (maybe just made a typo) did not provide valid input is controlling your flow to error handling. But this case is not at all "exceptional". In fact, you should expect it. int.TryParse makes this possible, in that it returns you a flag (boolean) that informs you about success or failure of the conversion attempt (instead of throwing).

Though I would recommend you to learn if else loop first https://www.w3schools.com/cs/cs_conditions.asp
here is the code if needed
int[] usernum = new int[4];
for (int i = 0; i < usernum.Length; i++)
{
var result = Console.ReadLine();
int currentResult;
if (!int.TryParse(result, out currentResult))
{
Console.WriteLine("Invalid input - must be a valid integer value");
i--;
continue;
}
if(currentResult < 1 || currentResult > 25)
{
Console.WriteLine("Invalid input - must be between 1 & 25");
i--;
continue;
}
usernum[i] = currentResult;
}

for-loop might not be the ideal solution for this use-case where you need to conditionally increment the index.
This should do the trick:
int[] userNumbers = new int[5];
int i = 0;
while (i < userNumbers.Length)
{
string rawInput = Console.ReadLine();
bool isNumberValid = int.TryParse(rawInput, out int inputNumber); // as suggested by #Fildor
if(isNumberValid && inputNumber >= 1 && inputNumber <= 25) // increment counter only if 1 <= input <= 25
{
userNumbers[i] = inputNumber;
i++;
}
}

How can I set values in a 2D array from keyboard

I´m working on some codes in C# for school. But there is this exercise that is huge headache.
This is it: I have to develope a code that allows the user to set a value (put in an x) for a 2D array (5x5) from the keyboard. This means that when running the program the user should be able to set one value inside the array, something like "I wana set an "x" in 2,5 and 3,1". I just have no clue how to do that. it´s been already two weeks but i can´t figure it out.
This is what i have so far (updated, thnx to all, specially BradleyDotNET for support):
int[,] data = new int[5, 5];
public void load()
{
string[] input = Console.ReadLine().Split('=');
string[] coordinates = input[0].Split(',');
int[] intCoordinates = coordinates.Select(s => int.Parse(s)).ToArray();
data[intCoordinates[0]][intCoordinates[1]] = int.Parse(input[1]);
}
public void view()
{
Console.WriteLine("Matrix created is:");
for (int i = 0; i <= 4; i++)
{
Console.Write("\n");
for (int j = 0; j <= 4; j++)
{
Console.Write(data);
}
}
Console.ReadKey();
}
static void Main(string[] args)
{
Program objeto = new Program();
objeto.load();
objeto.view();
Console.ReadKey();
Console.Clear();
I also have to add a feature to let the user add as many "x" to the matriz as he wants, but im planning to do that with a "switch".
So, How do you set values inside the 2d array from keyboard?
Update: The mistake i get here is in line 10, inside "data". It says "Incorrect index number inside []. 2 was expected"

You didn't specify the format the input, so I"ll make one up. If the input was "2,4=10" (meaning set element[2][4] to 10), the code would be:
string[] input = Console.ReadLine().Split('=');
string[] coordinates = input[0].Split(',');
int[] intCoordinates = coordinates.Select(s => int.Parse(s)).ToArray();
matrix[intCoordinates [0]][intCoordinates [1]] = int.Parse(input[1]);
This code has a few problems with it, there is no range validation and if the user enters anything other than an int, it will throw. I'll leave those as an exercise to you, but feel free to ask if you run into trouble.
To explain, we use Console.ReadLine to get a whole line of input. Then we break it on the '=' character to get our coordinates and desired value. We then split the coordinates on ',' to get the different indices.
You can't use strings as array indices, so we call Select to invoke the int.Parse() function on each string, returning us a new array of ints.
Finally, we use the parsed indices to index into matrix and set it to the parsed value from the input.

Something like this should help you.
public void load()
{
for (int i = 0; i <= 4; i++)
{
for (int j = 0; j <= 4; j++)
{
Console.WriteLine("enter value for {0},{1}", i, j);
matrix[i,j]= int.Parse(Console.ReadLine());
}
}
}
BTW, in your view method start the loop from 0 to 4

2d array,adding it values in a weird pattern

i started learning C# and programming a few months ago and have some problems. The idea here is we create a 2 dimensional array (the number of rows / columns are added by the user), the numbers need to be between 1 and 10.
Then when the array is created the number sequence ( 3-5-7-9-11 etc) is started in the first and finishes in the last column. The rest of the numbers in the columns are added via keyboard by the user starting with the first row (ignoring column 1 and the last column cause we have that added).
The questions are :
What will be the best way to check if the numbers of rows/columns are between 1 and 10? (I was thinking of IF-else but isn't there a better way ?)
How will i make it so that the number sequence 3-5-7 etc is started in the first and finishes in the last column?
Yeah i feel lost.
Where i am at the moment :
Console.WriteLine("Add row value of 1-10");
string s1
s1 = Console.ReadLine();
int k = int.Parse(s1);
Console.WriteLine("Add column value of 1-10");
string s2;
s2 = Console.ReadLine();
int p = int.Parse(s2);
int[,] M = new int[k, p];
Example : we added k(row) & p(coulmn) value of 4.So the array should look like :
3 x x 11
5 x x 13
7 x x 15
9 x x 17
Then the X's should be added again manually without overwriting the existing numbers .The value of the numbers doesnt matter.

So... If I get it right you want to ask user the "length and width" of dynamical 2d array?
To check if entered number is between 1 and 10 there's only 1 method:
int [,] M;
if (k >= 1 && k <= 10 && p >= 1 && p <= 10)
{
M = new int[k,p];
}
And better is to do int.TryParse() for case if user enters characters there instead of numbers, or else you can easily get an Exception.
Filling with numbers:
int num = 3;
for (int i = 0; i < k; ++i)
{
M[i,0] = num;
num+=2;
}
for (int i = 0; i < k; ++i)
{
M[i,p] = num;
num+=2;
}
This adds numbers in 1st and last column in each row. After that to fill other cells manually you check every cell thet it is not in firs or last column.
I hope I understood you correctly. Provided code may be simplified, but provided in such way for better understanding.

if(k>0 && k<11 && p>0 && p<11)
{
int i;
int M[,] = new int[k,p];
for (i=0;i<k;i++)
{
M[i,0]=i*2+3;
M[i,p-1]=(i+k)*2+3;
}
}

Time complexity of a powerset generating function

I'm trying to figure out the time complexity of a function that I wrote (it generates a power set for a given string):
public static HashSet<string> GeneratePowerSet(string input)
{
HashSet<string> powerSet = new HashSet<string>();
if (string.IsNullOrEmpty(input))
return powerSet;
int powSetSize = (int)Math.Pow(2.0, (double)input.Length);
// Start at 1 to skip the empty string case
for (int i = 1; i < powSetSize; i++)
{
string str = Convert.ToString(i, 2);
string pset = str;
for (int k = str.Length; k < input.Length; k++)
{
pset = "0" + pset;
}
string set = string.Empty;
for (int j = 0; j < pset.Length; j++)
{
if (pset[j] == '1')
{
set = string.Concat(set, input[j].ToString());
}
}
powerSet.Add(set);
}
return powerSet;
}
So my attempt is this:
let the size of the input string be n
in the outer for loop, must iterate 2^n times (because the set size is 2^n).
in the inner for loop, we must iterate 2*n times (at worst).
1. So Big-O would be O((2^n)*n) (since we drop the constant 2)... is that correct?
And n*(2^n) is worse than n^2.
if n = 4 then
(4*(2^4)) = 64
(4^2) = 16
if n = 100 then
(10*(2^10)) = 10240
(10^2) = 100
2. Is there a faster way to generate a power set, or is this about optimal?

A comment:
the above function is part of an interview question where the program is supposed to take in a string, then print out the words in the dictionary whose letters are an anagram subset of the input string (e.g. Input: tabrcoz Output: boat, car, cat, etc.). The interviewer claims that a n*m implementation is trivial (where n is the length of the string and m is the number of words in the dictionary), but I don't think you can find valid sub-strings of a given string. It seems that the interviewer is incorrect.
I was given the same interview question when I interviewed at Microsoft back in 1995. Basically the problem is to implement a simple Scrabble playing algorithm.
You are barking up completely the wrong tree with this idea of generating the power set. Nice thought, clearly way too expensive. Abandon it and find the right answer.
Here's a hint: run an analysis pass over the dictionary that builds a new data structure more amenable to efficiently solving the problem you actually have to solve. With an optimized dictionary you should be able to achieve O(nm). With a more cleverly built data structure you can probably do even better than that.

2. Is there a faster way to generate a power set, or is this about optimal?
Your algorithm is reasonable, but your string handling could use improvement.
string str = Convert.ToString(i, 2);
string pset = str;
for (int k = str.Length; k < input.Length; k++)
{
pset = "0" + pset;
}
All you're doing here is setting up a bitfield, but using a string. Just skip this, and use variable i directly.
for (int j = 0; j < input.Length; j++)
{
if (i & (1 << j))
{
When you build the string, use a StringBuilder, not creating multiple strings.
// At the beginning of the method
StringBuilder set = new StringBuilder(input.Length);
...
// Inside the loop
set.Clear();
...
set.Append(input[j]);
...
powerSet.Add(set.ToString());
Will any of this change the complexity of your algorithm? No. But it will significantly reduce the number of extra String objects you create, which will provide you a good speedup.