How to add a space before and after conditional operator in a string?

user_1611712 0
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I have a string e.g "number1<=number2&&number3>number4||number2=number4" and having operator list as -

var operators = new List<string> {"=", "!", "<", ">", ">=", "<=", "!=","||","&&"};

So, expectation is to introduce a single space before and after each operator in the string.

"number1 <= number2 && number3 > number4 || number2 = number4"

I tried following code but its not working for instance, e.g, <, >=

public static string AddSpaceBeforeAndAfterOperator(string expression) {
  var operators = new List<string> {"=", "!", "<", ">", ">=", "<=", "!=", "||", "&&"};
  foreach (var op in operators) {
    var index = expression.IndexOf(op, StringComparison.Ordinal);
    if (index >= 0) {
      if (expression.Substring(index - 1) != " ") {
        expression = expression.Insert(index-1, " ");
      }
    expression = expression.Insert(index + op.Length + 1, " ");
    }
  }
  return expression;
}

Note: The Operator list is coming as random.

Any help would be appreciated!

c#-4.0 string c#
2 Answers

I would recommend a regex solution.

First, you need to escape all your operators, join them together with |:

var operatorsString = string.Join("|", 
    operators.OrderByDescending(x => x.Length).Select(Regex.Escape).ToArray()
);
// OrderByDescending here because we want the longer operators to be matched first.

Next, create the regex:

var regex = $"\\s*({operatorString})\\s*";

Using the operators array in the question, the array looks like this:

\s*(<=|>=|!=|==|\|\||&&|=|!|<|>)\s?*

Note that \s* is used to check if the operator is already surrounded by spaces. If it is, those spaces will be matched and replaced.

The replacement is:

 $1

Code:

Regex.Replace(input, regex, " $1 ");

Note the leading and trailing space.

Also note that Regex is inside the System.Text.RegularExpressions namespace.

Demo

user_51335850

Im not sure if this is the most effective way to do this, but is is rally simple by using replace

public static string AddSpaceBeforeAndAfterOperator(string expression)
{
    var operators = new List<string> { "=", "!", "<", ">", ">=", "<=", "!=", "||", "&&" };
    foreach (var op in operators)
    {
        expression = expression.Replace(op, " " + op + " ");
    }

    return expression;
 }
user_64081560
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