How can i assign a value to a char variable in a foreach loop? C#

Question

I am trying to do is something like this:

StringBuilder sb = new StringBuilder();
foreach(char ch in valor)
{
 if (ch == ',')
 ch = '.';
 else if (ch == '0' || ch == '1' || ch == '2' || ch == '3' || ch == '4' || ch == '5' || ch == '6' || ch == '7' || ch == '8' || ch == '9' || ch == ',')
 {
 sb.Append(ch);
 }
}

What I want is, if the character is a comma, to make it a dot. But i get the following error

it is not possible to assign value to 'ch' because it is a foreach interaction variable

• Guru Stron: What is the end goal? Also ch == ',' is present both in if and else if which does not make much sense.
• Sinatr: Possible duplicate.
• Fildor: The lang spec explicitly states "The variable v is read-only in the embedded statement." but not why. learn.microsoft.com/en-us/dotnet/csharp/language-reference/…
• fubo: alternative approaches if ("0123456789.".Contains(ch)) or if (char.IsDigit(ch) || ch == '.')

Answer 1

Why not append in both if branches?

foreach(char ch in valor)
{
 if (ch == ',')
 {
 sb.Append('.');
 }
 else if (ch == '0' || ch == '1' || ch == '2' || ch == '3' || ch == '4' || ch == '5' || ch == '6' || ch == '7' || ch == '8' || ch == '9')
 {
 sb.Append(ch);
 }
}

• Fildor: Or use string.Replace( ",", ".") prior to the foreach?
• Gabriel Dias: Oh God, don't know how I didn't think about it... Thanks!
• EricSchaefer: @Fildor Yes, that's how I would do it, but the question was a little different. There are probably 100 million ways to do it.
• Fildor: Absolutely. It's just the first thing that came to my mind... Also, to me the question seems a little like "how can I do x, while I am not allowed to do x" ... so hard to answer, anyway.

Answer 2

Short answer: it is impossible.

Using an immutable foreach indexed item you need to use an intermediate variable like that:

foreach ( char ch in valor )
{
 char c = ch;
 if ( c == ',' )
 {
 c = '.';
 }
 if ( c == '0' || c == '1' || c == '2' || c == '3' || c == '4'
 || c == '5' || c == '6' || c == '7' || c == '8' || c == '9'
 || c == '.' )
 {
 sb.Append(c);
 }
}

I removed the else because it seems to be a mistake...

But in this case you may prefer directly use a for to avoid this useless intermediate variable and so to optimize speed and memory:

for (int index = 0; index < valor.Length; index++)
{
 char c = valor[index];
 if ( c == ',' )
 {
 c = '.';
 }
 if ( c == '0' || c == '1' || c == '2' || c == '3' || c == '4'
 || c == '5' || c == '6' || c == '7' || c == '8' || c == '9'
 || c == '.' )
 {
 sb.Append(c);
 }
}

Next, in the case of the code provided, we can refactor like that, using the else in the right way now:

for (int index = 0; index < valor.Length; index++)
{
 char c = valor[index];
 if ( c == ',' )
 {
 sb.Append('.');
 }
 else
 if ( c == '0' || c == '1' || c == '2' || c == '3' || c == '4'
 || c == '5' || c == '6' || c == '7' || c == '8' || c == '9' )
 {
 sb.Append(c);
 }
}

Also, in the case of the code provided, we can improve to this:

for ( int index = 0; index < valor.Length; index++ )
{
 char c = valor[index];
 if ( c == ',' )
 {
 sb.Append('.');
 }
 else
 if ( char.IsDigit(c) ) // or IsNumber
 {
 sb.Append(c);
 }
}

And to optimize better:

for ( int index = 0; index < valor.Length; index++ )
{
 char c = valor[index];
 if ( c == ',' )
 {
 sb.Append('.');
 }
 else
 if ( c >= '0' && c <= '9' )
 {
 sb.Append(c);
 }
}

So using a foreach we can write, but a little less optimized while being more clean:

foreach (char ch in valor )
{
 if ( ch == ',' )
 {
 sb.Append('.');
 }
 else
 if ( ch >= '0' && ch <= '9' )
 {
 sb.Append(ch);
 }
}

Char.IsDigit Method

Char.IsNumber Method

foreach, in (C# reference)

for (C# reference)

Answer 3

Just introduce a local variable

StringBuilder sb = new StringBuilder();
foreach(char ch in valor)
{
 var tmp = ch == ',' ? '.' : ch;
 if (char.IsDigit(tmp) || tmp == '.')
 {
 sb.Append(tmp);
 }
}

You can also use the static char.IsDigit() method to check whether a char is a digit or not

You could also do it only with linq:

var sb = new StringBuilder();
sb = valor
 .Select(c => c == ',' ? '.' : c)
 .Where(c => char.IsDigit(c) || c == '.')
 .Aggregate(sb, (sb, c) => sb.Append(c));

Answer 4

You can try this:

StringBuilder sb = new StringBuilder();
var valor = "google,com1234";
if (valor.Contains(','))
{
 valor = valor.Replace(",", ".");
}
foreach (char ch in valor)
{
 if (ch == '0' || ch == '1' || ch == '2' || ch == '3' || ch == '4' || ch == '5' || ch == '6' || ch == '7' || ch == '8' || ch == '9' || ch == '.')
 {
 sb.Append(ch);
 }
}