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How to create regular expression only accept special formula?
Regular expressions are powerful patterns used to validate and match specific text formats. In this tutorial, we'll learn how to create regular expressions that validate mathematical formulas containing various operators and formats.
Basic Formula Validation
Let's start with a simple regular expression that accepts basic mathematical formulas with addition and subtraction operators.
Syntax
let regex = /^\d+([-+]\d+)*$/g;
This regex accepts formulas like "10-13+12+23" with no spaces between operators and numbers.
Regular Expression Breakdown
^ - Represents the start of the string
\d+ - Matches one or more digits at the beginning
[-+] - Matches either '+' or '-' operators
([-+]\d+)* - Matches zero or more occurrences of operator followed by digits
$ - Represents the end of the string
g - Global flag to match all occurrences
Example: Basic Addition and Subtraction
<html>
<body>
<h3>Validating Basic Mathematical Formulas</h3>
<div id="output"></div>
<script>
let output = document.getElementById('output');
function validateBasicFormula(formula) {
let regex = /^\d+([-+]\d+)*$/g;
let isMatch = regex.test(formula);
if (isMatch) {
output.innerHTML += "? '" + formula + "' matches the pattern<br>";
} else {
output.innerHTML += "? '" + formula + "' does not match the pattern<br>";
}
}
validateBasicFormula("10+20-30-50"); // Valid
validateBasicFormula("60*70*80"); // Invalid (contains *)
validateBasicFormula("10 + 20 - 30"); // Invalid (contains spaces)
</script>
</body>
</html>
? '10+20-30-50' matches the pattern ? '60*70*80' does not match the pattern ? '10 + 20 - 30' does not match the pattern
Advanced Formula with All Operators and Spaces
For more complex formulas that include multiplication, division, and optional whitespace, we use a more comprehensive pattern:
let regex = /^\d+(\s*[-+*/]\s*\d+)*$/g;
Enhanced Pattern Explanation
^\d+ - One or more digits at the start
\s* - Zero or more whitespace characters
[-+*/] - Matches +, -, *, or / operators
(\s*[-+*/]\s*\d+)* - Zero or more occurrences of: optional spaces, operator, optional spaces, and digits
Example: Complete Mathematical Formulas
<html>
<body>
<h3>Validating Complete Mathematical Formulas</h3>
<div id="output"></div>
<script>
let output = document.getElementById('output');
function validateCompleteFormula(formula) {
let regex = /^\d+(\s*[-+*/]\s*\d+)*$/g;
let isMatch = regex.test(formula);
if (isMatch) {
output.innerHTML += "? '" + formula + "' is a valid formula<br>";
} else {
output.innerHTML += "? '" + formula + "' is invalid<br>";
}
}
validateCompleteFormula("123 + 454 - 565 * 23"); // Valid
validateCompleteFormula("41*14* 90 /80* 70 + 90"); // Valid
validateCompleteFormula("41*14& 90 ^80* 70 + 90"); // Invalid (contains & and ^)
</script>
</body>
</html>
? '123 + 454 - 565 * 23' is a valid formula ? '41*14* 90 /80* 70 + 90' is a valid formula ? '41*14& 90 ^80* 70 + 90' is invalid
Comparison of Approaches
| Pattern | Operators Supported | Spaces Allowed | Use Case |
|---|---|---|---|
/^\d+([-+]\d+)*$/g |
+ and - only | No | Basic arithmetic |
/^\d+(\s*[-+*/]\s*\d+)*$/g |
+, -, *, / | Yes | Complete formulas |
Common Use Cases
Form Validation - Validating calculator input fields
Expression Parsers - Pre-validating mathematical expressions
Educational Tools - Checking student math input formats
Conclusion
Regular expressions provide a powerful way to validate mathematical formulas. Use the basic pattern for simple arithmetic and the advanced pattern for comprehensive formula validation including all operators and optional whitespace.
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