Errors in Apps Checking Prime Number

Quang Dinh Luong

11y1kC# Corner

This is how my program looks like, sorry for bad arrangement

I get this error: Cannot implicity convert type "string" to "int"

Anyone knows how to fix it? Your help'll be very appriciated

namespace IsThisPrime

{

public partial class Form1 : Form

{

public Form1()

{

InitializeComponent();

}

private void button1_Click(object sender, EventArgs e)

{

int x = textBox1.Text;

int i = 0;

bool Flag = false;

for (i = 2; i <= x / 2; i++)

{

if ((i == x))

i = i + 1;

if ((x % i == 0))

{

Flag = true;

break;

}

if ((Flag == false))

{

// this num is prime number

MessageBox.Show("PRIME");

}

else

{

// this num is not prime number

MessageBox.Show("NOT PRIME");

}

12 Replies

Know the answer? Post it — somebody with the same question will find it here.

Priyaranjan K S11y ago
Accepted answer
Hi,

You cannot implicitly convert a string to integer . The problem lies here :
int x = textBox1.Text;

Explicitly typecast the text box value to int as below and it should work
int x =Int32.Parse(textBox1.Text);

Thanks,
Priyan

If you found this useful Please mark this as Answer
Priyaranjan K S11y ago
Cool.. Cheers..
Quang Dinh Luong11y ago
Oh, it turns out, because I copied paste your code so there must be an error, now I fix it, it works fine now, thank you very much
Priyaranjan K S11y ago
Hi,

I tried out this code in the console and got the output highlighted.
int num1;
bool check= int.TryParse(text1, out num1);
if (!check)
{
Console.WriteLine(check);
}
else
{
Console.WriteLine(check);
}
False
string text1 = "4";
int num1;
bool check= int.TryParse(text1, out num1);
if (!check)
{
Console.WriteLine(check);
}
else
{
Console.WriteLine(check);
}
True

Thanks,
Priyan
Quang Dinh Luong11y ago
I'm sorry but the bool is always return value false whether the input is int or not. Is there another way?
Priyaranjan K S11y ago
Hi,

If you want to limit the input to just numbers we can use the same code .

string text1 = "x";
int num1;
bool check= int.TryParse(text1, out num1);
if (!check)
{
MessageBox.Show("I can just check NUMBERS");
}
else
{
MessageBox.Show(num1+ "is a number");
}

int.TryParse can be used to catch the error as above . If you need more help feel free to reach out .

Thanks,
Priyan
Quang Dinh Luong11y ago
When i said includes string I mean any other kinds that not number
Quang Dinh Luong11y ago
I'm learning to make my program stable, so... please help me with this! :)
As you know that this app can just with input is number, and if the input was string, the app fails.
Do you know a way to make an exception for that? I mean (in my dream):

if (textBox1.Text includes string)
{
MessageBox.Show("I can just check NUMBERS");
}
else
{
My content;
}
Quang Dinh Luong11y ago
One more crazy question!
I know that int64 has the max value of 9,223,372,036,854,775,807
I mean this is still limited
I wonder if there is a way that the input is unlimited???
Priyaranjan K S11y ago
No Probs . Happy to help .

You might have got the error that you cannot convert int to long this time . This is because Int64.Parse tries to convert the string to a 64 bit signed integer . So you need an equivalent typecasted variable to hold the value preferably a variable of the type 'long'

try this code :
long x = Int64.Parse(textBox1.Text);

Thanks,
Priyan
Quang Dinh Luong11y ago
I'm greateful for your help! Sorry for being shabby, but can't I:

int x = Int64.Parse(textBox1.Text);

I mean I want the app can handle more numbers. But the IDE marks it as error, can you tell me why and how to fix it?
Priyaranjan K S11y ago
The above code will work . A better implementation would be to use 'TryParse' .This is because if text box contains a string and we try to parse it using 'Int32.Parse' , the code will break . However TryParse returns a boolean value which contains true if the conversion is successful as well as the converted number . It returns false if the conversion was not successful .

string text1 = "x";
int num1;
bool res = int.TryParse(text1, out num1);
if (res == false)
{
// String is not a number.
}
else
{
// Write rest of the functionality here
}

Thanks,
Priyan

If you found this useful Please mark this as Answer