How can I use a foreach statement to loop between 2 values given by the user?
I am making an application that scans for ports, so I want the user to specify which ports to search for; here is some example code that dose not function, but should help you understand what I am looking for:
int port1 = Int32.Parse(TextBox1.Text);
int port2 = Int32.Parse(TextBox2.Text);
foreach(int between port1 and port2)
{
//do something
}
Any suggestions on how I could do this ?
No, foreach is for iterating over a collection. What you want is a for loop.
int port1 = Int32.Parse(TextBox1.Text);
int port2 = Int32.Parse(TextBox2.Text);
for(var i = port1; i <= port2; i++)
{
//do something
}
AlexD's answer is on the right track, but unfortunately misuses the second parameter of Enumerable.Range. The second parameter is count, not a bound for the range.
It should read:
Enumerable.Range(port1, (port2 - port1) + 1)
or if you don't know if port1 is less than port2:
Enumerable.Range(Math.Min(port1, port2), Math.Abs(port2 - port1) + 1)
Related
I have a simple question that I can't find a clean answer to when I google.
How do I iterate a foreach loop between index 40-60 and get the values for the indexes?
List<int> list1 = new List<int>();
for (int i = 0; i < 100; i++)
{
list1.Add(i);
}
foreach (var i in list1)
{
//How to iterate between index: 40 to 60 ?
}
The easiest approach would be to use a regular for loop:
for (int i = 40; i < 60; ++i)
{
int value = list1[i];
// Do something with the value
}
Note - if you want to get the value for index 60 too (i.e., the range is inclusive), you should use the <= operator instead of <.
Foreach loop doesn't use an index for traversing an array or collection. They take advantage of the enumerator in an IEnumerable. This answer here has a great explanation of that.
If you want you can add an int before the foreach loop and increment within the loop, but that's all you can do. I would advise that you filter your list1 beforehand and then use it in the foreach loop.
If you really want to use a foreach then you need to write this
List<int> list1 = new List<int>();
foreach(int i in Enumerable.Range(40, 20))
{
list1.Add(i);
}
But, lacking better info on your request to use foreach, then I agree to use a standard for-loop
Aside from other more appropriate answers (e.g. just use a for loop), here's a solution that uses the .Where() overload that provides the index of the element as a parameter to the predicate:
foreach (var i in list1.Where((x, index) => index >= 40 && index <= 60))
{
//How to iterate between index: 40 to 60 ?
}
I've been working on a project where I need on a button press that this line gets executed.
if (listView1.SelectedItems[0].SubItems[3].Text == "0") //Checks to see Value
{
listView1.SelectedItems[0].SubItems[3].Text = "1";// If Value is Greater, Increase and Change ListView
questionNumberLabel.Text = listView1.SelectedItems[0].SubItems[3].Text;// Increase and Change Label
}
Now I have this repeated about 10 times with each value increasing by one. But I know that this is ugly, and dysfunctional. As well as conflates the file size. I've tried a few things. Primarily this method.
if (listView1.SelectedItems[0].SubItems[3].Text == "0")
{
for (var i = 1; i < 100;)
{
if (!Int32.TryParse(listView1.SelectedItems[0].SubItems[3].Text, out i))
{
i = 0;
}
i++;
listView1.SelectedItems[0].SubItems[3].Text = i.ToString();
Console.WriteLine(i);
}
}
But instead of just adding one, it does the 100 instances and ends. The reason this is becoming a pain in the *** is because the
listView1.SelectedItems[0].SubItems[3].Text
is just that - it's a string, not an int. That's why I parsed it and tried to run it like that. But it still isn't having the out come I want.
I've also tried this
string listViewItemToChange = listView1.SelectedItems[0].SubItems[3].Text;
Then parsing the string, to make it prettier. It worked like it did before, but still hasn't given me the outcome I want. Which to reiterate is, I'm wanting the String taken from the list view to be changed into an int, used in the for loop, add 1, then restring it and output it on my listView.
Please help :(
You say you want the text from a listview subitem converted to an int which is then used in a loop
so - first your creating your loop variable, i, then in your loop you're assigning to it potentially 3 different values 2 of which are negated by the, i++. None of it makes sense and you shouldn't be manipulating your loop variable like that (unless understand what you're doing).
if you move statements around a little..
int itemsToCheck = 10; // "Now I have this repeated about 10 times "
for (var item = 0; item < itemsToCheck; item++)
{
int i;
if (!Int32.TryParse(listView1.SelectedItems[item].SubItems[3].Text, out i))
{
i = 0;
}
i++;
listView1.SelectedItems[item].SubItems[3].Text = i.ToString();
Console.WriteLine(i);
}
Something along those lines is what you're looking for. I haven't changed what your code does with i, just added a loop count itemsToCheck and used a different loop variable so your loop variable and parsed value are not one in the same which will likely be buggy.
Maybe this give you an idea. You can start using this syntax from C# 7.0
var s = listView1.SelectedItems[0].SubItems[3].Text;
var isNumeric = int.TryParse(s, out int n);
if(isNumeric is true && n > 0){
questionNumberLabel.Text = s;
}
to shortcut more
var s = listView1.SelectedItems[0].SubItems[3].Text;
if(int.TryParse(s, out int n) && n > 0){
questionNumberLabel.Text = s;
}
I'm having trouble thinking of a logical way to achieve this. I have a method which sends a web request with a for loop that is counting up from 1 to x, the request counts up until it finds a specific response and then sends the URL + number to another method.
After this, saying we got the number 5, I need to create a string which displays as "1,2,3,4,5" but cannot seem to find a way to create the entire string, everything I try is simply replacing the string and only keeping the last number.
string unionMod = string.Empty;
for (int i = 1; i <= count; i++)
{
unionMod =+ count + ",";
}
I assumed I'd be able to simply add each value onto the end of the string but the output is just "5," with it being the last number. I have looked around but I can't seem to even think of what I would search in order to get the answer, I have a hard-coded solution but ideally, I'd like to not have a 30+ string with each possible value and just have it created when needed.
Any pointers?
P.S: Any coding examples are appreciated but I've probably just forgotten something obvious so any directions you can give are much appreciated, I should sleep but I'm on one of those all-night coding grinds.
Thank you!
First of all your problem is the +=. You should avoid concatenating strings because it allocates a new string. Instead you should use a StringBuilder.
Your Example: https://dotnetfiddle.net/Widget/qQIqWx
My Example: https://dotnetfiddle.net/Widget/sx7cxq
public static void Main()
{
var counter = 5;
var sb = new StringBuilder();
for(var i = 1; i <= counter; ++i) {
sb.Append(i);
if (i != counter) {
sb.Append(",");
}
}
Console.WriteLine(sb);
}
As it's been pointed out, you should use += instead of =+. The latter means "take count and append a comma to it", which is the incorrect result you experienced.
You could also simplify your code like this:
int count = 10;
string unionMod = String.Join(",", Enumerable.Range(1, count));
Enumerable.Range generates a sequence of integers between its two parameters and String.Join joins them up with the given separator character.
I'm interested in doing something like this (C#):
int sum = 0;
for (int i = 0; i < 5; i++)
sum += i;
But I would like to do it on one line. Something like:
int sum = (embedded loop)
Is there any way to do this on one line? I'm looking to apply this to a more complex string manipulation algorithm so I can't simply replace the loop with an arithmatic formula.
So you want to loop and do something in one line?
First off, writing it in one line isn't going to make it run faster. You are still going to loop, you are still going to be O(n). For the particular problem you have in your question you can do something like:
var sum = Enumerable.Range(0,5).Sum();
This will basically make a collection of the numbers 0,1,2...4 and sum them.
More generally, since you want to do something, you might use the Aggregate function. For example:
var str = Enumerable.Range(0,5).Aggregate("",(p,c) => p + c); // Note: not efficient at all
Will take the values 0,1,...4 and do string concatenation with them (using a string builder would be better) to give you the string 01234.
Edit:
I'm trying to loop through a list of words and make each one title case, then return the string[].join(" ") of it
In that case, something like:
var result = string.Join(" ", myListOfWords.Select(w => char.ToUpper(w[0]) + w.Substring(1)));
Should work fine.
If you don't mind that 'sum' only is in scope of the for loop you could do this:
for (int i = 0, sum = 0; i < 5; sum += i, ++i) { // do something }
for(int i=0,sum = 0; i<5; sum+=i,++i){}
I'm writing code in C# and trying to add all of the numbers between the number 1 and N, N being the number that is inputted in a textbox. I'm doing this, at least trying to do this, by putting it into a while loop.
I have added all the numbers between 2 textboxes before but for some reason I'm driving myself crazy and can't figure this out. I'm a beginning programmer so please be gentle.
Any help would be greatly appreciated.
Edit:
One of the six thousand things I've tried. I think this has me in an infinite loop?
private void btnAddAll_Click(object sender, EventArgs e)
{
int n;
int count = 0;
int answer = 0;
n = int.Parse(txtNum.Text);
count = n;
while (count >= 1)
{
answer = answer + count;
count++;
}
lstShow.Items.Add("Sum = " + answer);
lstShow.Text = answer.ToString();
}
Why not use Gauss formula. (N*(N+1))/2
private void btnAddAll_Click(object sender, EventArgs e)
{
int n, answer;
n = int.Parse(txtNum.Text);
answer = (n*(n+1))/2;
lstShow.Items.Add("Sum = " + answer);
lstShow.Text = answer.ToString();
}
If you change the ++ to a -- it should work as you want it to.
int n;
int count = 0;
int answer = 0;
n = 3;
count = n;
while (count >= 1)
{
answer = answer + count;
count--; // here was the error
}
Console.WriteLine (answer);
Output: 6
Also, just for a point of additional interest you can use That uses Enumerable.Range and Enumerable.Sum instead of the while loop (probably goes beyond what is expected for a homework but it's useful to know what's out there).
answer = Enumerable.Range(1, n).Sum();
Your edit: you should decrement count..
Another edit, it appears I need to explain more:
By decrement I mean --. The post or pre decrement operator decreases the value by 1.
If count keeps increasing by 1, count >=1 will never be met. You need to reduce count to 1.. hence count--;
Also I suggest you use TryParse(string,out int) ; or at least wrap the Parse call in a try catch block.
Here is a pointer in pseudocode:
GetInput From User
TryParse Input
If Between 1 and N
Declare sum = 1;
for i to N-1
sum+=i;
/* if you don't want to use the for loop
while i < N
sum+=i;
inc i; */
Print sum
Debugging is an important skill for any programmer. There are some good tools in Visual Studio to help with debugging.
A good way to debug your code when you are stuck is to use 'breakpoints' and step through the code.
Select the line you want your code to stop at (e.g. n = int.Parse(txtNum.Text);) and press F9 - this will add a breakpoint at this line.
Now, when you run your programme, it will stop at the breakpoint. If you press F11, you can 'step' through the code one line at a time. You can hold your mouse over a variable to see its value while you are doing this.
You will quickly find the problem in your code if you do this.