From d137d849ae8a51396462dfb0908b493e6b0c5a08 Mon Sep 17 00:00:00 2001
From: Suraj <surajh51985@gmail.com>
Date: Sat, 23 May 2026 16:03:35 +0530
Subject: [PATCH] fix: add input validation to prevent errors in calculator

Prevents division by zero, multiple decimal points, and consecutive operators.

- Added hasDecimalInCurrentNumber() validation
- Added hasConsecutiveOperators() validation
- Modified NumberButtonClick() and functionButton() with validation

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
---
 Calculator/Pratik1968/main.js | 105 +++++++++++++++++++++++++++++-----
 1 file changed, 92 insertions(+), 13 deletions(-)

diff --git a/Calculator/Pratik1968/main.js b/Calculator/Pratik1968/main.js
index 8ef9c5b53..d7e7f2766 100644
--- a/Calculator/Pratik1968/main.js
+++ b/Calculator/Pratik1968/main.js
@@ -1,29 +1,71 @@
-let value = ""
+let value = "";
 
-let ans = 0
+let ans = 0;
 
 
 function setInput() {
     let input = document.getElementById("ans");
-    input.value = value
+    input.value = value;
 }
 
-window.onload = function() {
-    setInput()
+window.onload = function () {
+    setInput();
+}
+
+// Validate input to prevent multiple decimal points
+function hasDecimalInCurrentNumber() {
+    // Get the last number in the expression (after last operator)
+    const lastOperatorIndex = Math.max(
+        value.lastIndexOf('+'),
+        value.lastIndexOf('-'),
+        value.lastIndexOf('x'),
+        value.lastIndexOf('/'),
+        value.lastIndexOf('^'),
+        value.lastIndexOf('%')
+    );
+    const lastNumber = value.substring(lastOperatorIndex + 1);
+    return lastNumber.includes('.');
+}
+
+// Validate input to prevent consecutive operators
+function hasConsecutiveOperators() {
+    if (value.length === 0) return false;
+    const lastChar = value[value.length - 1];
+    return ['+', '-', 'x', '/', '^', '%'].includes(lastChar);
+}
+
+// Check if expression ends with a number
+function endsWithNumber() {
+    if (value.length === 0) return false;
+    const lastChar = value[value.length - 1];
+    return !isNaN(parseFloat(lastChar)) && isFinite(lastChar);
 }
 
 function NumberButtonClick(number) {
     let lastChar = value[value.length - 1];
 
+    // Prevent division by zero - if last char is '/' and user clicks 0, show error
     if (lastChar === '/' && number === 0) {
         alert("Error: Division by zero is undefined.");
         return null;
-    } else {
-        value += number
     }
 
+    // Prevent multiple decimal points in current number
+    if (number === '.' && hasDecimalInCurrentNumber()) {
+        alert("Error: Multiple decimal points are not allowed.");
+        return null;
+    }
 
-    setInput()
+    // Prevent consecutive operators - if last char is operator and user clicks another operator (not decimal)
+    if (hasConsecutiveOperators() && number !== '.') {
+        // Replace the last operator with the new one
+        value = value.slice(0, -1) + number;
+        setInput();
+        return null;
+    }
+
+    value += number;
+    setInput();
 }
 
 function isOperator(value) {
@@ -40,10 +82,33 @@ function functionButton(Function) {
     if (input.value == "" || input.value == null) { return; }
     let lastChar = value[value.length - 1];
 
+    // Prevent adding operator if expression already ends with an operator
     if (isOperator(lastChar) && Function !== '8') {
-        return;
+        // Allow decimal point even after operator
+        if (Function === '11') { // decimal button check
+            // handled separately
+        } else {
+            return;
+        }
     }
 
+    // Validate before evaluation
+    if (Function === functionVar.equal) {
+        // Check for trailing operators before evaluating
+        if (isOperator(lastChar)) {
+            alert("Error: Expression cannot end with an operator.");
+            return;
+        }
+        // Check for division by zero in the expression
+        if (value.includes('/0') && !value.includes('/0.')) {
+            // More rigorous check: if we have /0 not followed by a decimal digit
+            const divZeroPattern = /\/0(?![0-9])/;
+            if (divZeroPattern.test(value)) {
+                alert("Error: Division by zero is undefined.");
+                return;
+            }
+        }
+    }
 
     switch (Function) {
         case functionVar.add:
@@ -59,8 +124,13 @@ function functionButton(Function) {
                 value += "x";
             break;
         case functionVar.equal:
-            ans = eval(value.replace("x", "*").replace("%", "*1/100").replace("^", "**"));
-            value = ans;
+            try {
+                ans = eval(value.replace("x", "*").replace("%", "*1/100").replace("^", "**"));
+                value = ans;
+            } catch (e) {
+                alert("Error: Invalid expression.");
+                value = "";
+            }
             break;
         case functionVar.division:
             if (lastChar !== "/")
@@ -81,12 +151,21 @@ function functionButton(Function) {
             value = value.slice(0, -1)
             break;
         case functionVar.decimal:
-            if (lastChar !== "." && !value.includes('.'))
+            // Check if current number already has a decimal
+            if (hasDecimalInCurrentNumber()) {
+                alert("Error: Multiple decimal points are not allowed.");
+                return;
+            }
+            // If last char is operator, start new number with 0.
+            if (isOperator(lastChar) || value.length === 0) {
+                value += "0.";
+            } else {
                 value += ".";
+            }
             break;
     }
 
 
     setInput()
 
-}
\ No newline at end of file
+}