<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta name="description" content="VB6Parse Library Reference - asc - String">
<title>asc - String - VB6Parse Library Reference</title>
<link rel="stylesheet" href="../../../assets/css/style.css">
<link rel="stylesheet" href="../../../assets/css/docs-style.css">
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/11.9.0/styles/github-dark.min.css">
<script src="../../../assets/js/theme-switcher.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/11.9.0/highlight.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/11.9.0/languages/vbnet.min.js"></script>
<script>hljs.highlightAll();</script>
</head>
<body>
<header class="docs-header">
<div class="container">
<h1><a href="../../../index.html">VB6Parse</a> / <a href="../../../library/index.html">Library</a> / <a href="../../../library/functions/string/index.html">String</a> / asc</h1>
<p class="tagline">VB6 Library Reference</p>
</div>
</header>
<nav class="docs-nav">
<div class="container">
<a href="../../../index.html">Home</a>
<a href="../../../library/index.html">Library Reference</a>
<a href="../../../documentation.html">Documentation</a>
<a href="https://docs.rs/vb6parse" target="_blank">API Docs</a>
<a href="https://github.com/scriptandcompile/vb6parse" target="_blank">GitHub</a>
<button id="theme-toggle" class="theme-toggle" aria-label="Toggle theme">
<span class="theme-icon">🌙</span>
</button>
</div>
</nav>
<main class="container">
<article class="library-item">
<h1 id="asc-function">Asc Function</h1>
<p>Returns an <code>Integer</code> representing the character code corresponding to the first letter in a string.</p>
<h2 id="syntax">Syntax</h2>
<pre><code class="language-vbnet">Asc(string)</code></pre>
<h2 id="parameters">Parameters</h2>
<ul>
<li><code>string</code> - Required. Any valid string expression. If the string contains no characters, a run-time error occurs.</li>
</ul>
<h2 id="return-value">Return Value</h2>
<p>Returns an <code>Integer</code> representing the <code>ANSI</code> character code of the first character in the string.
- For <code>ANSI</code> characters (0-127), returns standard <code>ASCII</code> values
- For extended <code>ANSI</code> characters (128-255), returns extended <code>ASCII</code> values
- Unicode characters are converted to <code>ANSI</code> before the code is returned</p>
<h2 id="remarks">Remarks</h2>
<p>The <code>Asc</code> function returns the numeric <code>ANSI</code> character code for the first character in a string.
This is useful for:
- Validating input characters
- Performing character-based operations
- Converting characters to their numeric representations
- Character range checking</p>
<h3 id="important-notes">Important Notes</h3>
<ol>
<li><strong>Only First Character</strong>: Only the first character of the string is examined</li>
<li><strong>Empty String Error</strong>: Passing an empty string results in a run-time error (Error 5: Invalid procedure call or argument)</li>
<li><strong>ANSI vs. Unicode</strong>: In VB6, <code>Asc</code> returns <code>ANSI</code> codes; <code>AscW</code> returns Unicode values</li>
<li><strong>Return Type</strong>: Returns <code>Integer</code> (16-bit signed), range -32,768 to 32,767, but character codes are 0-255</li>
<li><strong>Case Sensitive</strong>: Upper and lowercase letters have different codes (e.g., "A" = 65, "a" = 97)</li>
</ol>
<h3 id="character-code-ranges">Character Code Ranges</h3>
<ul>
<li><strong>0-31</strong>: Control characters (non-printable)</li>
<li><strong>32</strong>: Space</li>
<li><strong>48-57</strong>: Digits '0' through '9'</li>
<li><strong>65-90</strong>: Uppercase letters 'A' through 'Z'</li>
<li><strong>97-122</strong>: Lowercase letters 'a' through 'z'</li>
<li><strong>128-255</strong>: Extended ANSI characters</li>
</ul>
<h2 id="examples">Examples</h2>
<h3 id="basic-usage">Basic Usage</h3>
<pre><code class="language-vbnet">Dim code As Integer
code = Asc("A") ' Returns 65
code = Asc("Apple") ' Returns 65 (first character only)
code = Asc("a") ' Returns 97
code = Asc("0") ' Returns 48
code = Asc(" ") ' Returns 32 (space)</code></pre>
<h3 id="character-validation">Character Validation</h3>
<pre><code class="language-vbnet">Function IsDigit(ch As String) As Boolean
Dim code As Integer
code = Asc(ch)
IsDigit = (code >= 48 And code <= 57)
End Function
Function IsUpperCase(ch As String) As Boolean
Dim code As Integer
code = Asc(ch)
IsUpperCase = (code >= 65 And code <= 90)
End Function</code></pre>
<h3 id="case-conversion-offset">Case Conversion Offset</h3>
<pre><code class="language-vbnet">' Calculate offset between upper and lower case
Dim offset As Integer
offset = Asc("a") - Asc("A") ' Returns 32</code></pre>
<h3 id="character-range-checking">Character Range Checking</h3>
<pre><code class="language-vbnet">Function IsPrintable(ch As String) As Boolean
Dim code As Integer
code = Asc(ch)
IsPrintable = (code >= 32 And code <= 126)
End Function</code></pre>
<h3 id="string-encoding">String Encoding</h3>
<pre><code class="language-vbnet">Function EncodeString(s As String) As String
Dim i As Integer
Dim result As String
For i = 1 To Len(s)
If result <> "" Then result = result & ","
result = result & CStr(Asc(Mid(s, i, 1)))
Next i
EncodeString = result
End Function</code></pre>
<h2 id="common-patterns">Common Patterns</h2>
<h3 id="1-input-validation">1. Input Validation</h3>
<pre><code class="language-vbnet">If Asc(userInput) >= 48 And Asc(userInput) <= 57 Then
' First character is a digit
End If</code></pre>
<h3 id="2-alphabetic-checking">2. Alphabetic Checking</h3>
<pre><code class="language-vbnet">Dim code As Integer
code = Asc(UCase(letter))
If code >= 65 And code <= 90 Then
' It's a letter
End If</code></pre>
<h3 id="3-csv-parsing-helper">3. CSV Parsing Helper</h3>
<pre><code class="language-vbnet">If Asc(field) = 34 Then ' 34 is double quote
' Handle quoted field
End If</code></pre>
<h3 id="4-character-comparison">4. Character Comparison</h3>
<pre><code class="language-vbnet">If Asc(char1) < Asc(char2) Then
' char1 comes before char2 in ASCII order
End If</code></pre>
<h3 id="5-special-character-detection">5. Special Character Detection</h3>
<pre><code class="language-vbnet">Select Case Asc(ch)
Case 9 ' Tab
Case 10 ' Line feed
Case 13 ' Carriage return
Case 32 ' Space
End Select</code></pre>
<h3 id="6-keyboard-input-processing">6. Keyboard Input Processing</h3>
<pre><code class="language-vbnet">Private Sub Text1_KeyPress(KeyAscii As Integer)
If KeyAscii = 13 Then ' Enter key
' Process input
End If
End Sub</code></pre>
<h3 id="7-character-class-testing">7. Character Class Testing</h3>
<pre><code class="language-vbnet">Function IsControl(ch As String) As Boolean
Dim code As Integer
code = Asc(ch)
IsControl = (code < 32 Or code = 127)
End Function</code></pre>
<h3 id="8-simple-encryption">8. Simple Encryption</h3>
<pre><code class="language-vbnet">Function ROT13Char(ch As String) As String
Dim code As Integer
code = Asc(UCase(ch))
If code >= 65 And code <= 90 Then
code = ((code - 65 + 13) Mod 26) + 65
ROT13Char = Chr(code)
Else
ROT13Char = ch
End If
End Function</code></pre>
<h2 id="common-character-codes">Common Character Codes</h2>
<table>
<thead>
<tr>
<th>Character</th>
<th>Code</th>
<th>Description</th>
</tr>
</thead>
<tbody>
<tr>
<td>Null</td>
<td>0</td>
<td>Null character</td>
</tr>
<tr>
<td>Tab</td>
<td>9</td>
<td>Horizontal tab</td>
</tr>
<tr>
<td>LF</td>
<td>10</td>
<td>Line feed</td>
</tr>
<tr>
<td>CR</td>
<td>13</td>
<td>Carriage return</td>
</tr>
<tr>
<td>Space</td>
<td>32</td>
<td>Space</td>
</tr>
<tr>
<td>!</td>
<td>33</td>
<td>Exclamation mark</td>
</tr>
<tr>
<td>"</td>
<td>34</td>
<td>Double quote</td>
</tr>
<tr>
<td>0</td>
<td>48</td>
<td>Digit zero</td>
</tr>
<tr>
<td>9</td>
<td>57</td>
<td>Digit nine</td>
</tr>
<tr>
<td>A</td>
<td>65</td>
<td>Uppercase A</td>
</tr>
<tr>
<td>Z</td>
<td>90</td>
<td>Uppercase Z</td>
</tr>
<tr>
<td>a</td>
<td>97</td>
<td>Lowercase a</td>
</tr>
<tr>
<td>z</td>
<td>122</td>
<td>Lowercase z</td>
</tr>
<tr>
<td>DEL</td>
<td>127</td>
<td>Delete</td>
</tr>
</tbody>
</table>
<h2 id="error-handling">Error Handling</h2>
<pre><code class="language-vbnet">On Error Resume Next
code = Asc(inputString)
If Err.Number = 5 Then
' Empty string error
MsgBox "String cannot be empty"
End If</code></pre>
<h2 id="related-functions">Related Functions</h2>
<ul>
<li><code>AscB</code>: Returns the first byte of a string</li>
<li><code>AscW</code>: Returns the Unicode character code</li>
<li><code>Chr</code>: Returns the character for a given character code (inverse of Asc)</li>
<li><code>ChrB</code>: Returns a byte containing the character</li>
<li><code>ChrW</code>: Returns a Unicode character</li>
<li><code>InStr</code>: Finds the position of a character in a string</li>
<li><code>Mid</code>: Extracts a substring</li>
<li><code>Left</code>: Gets leftmost characters</li>
<li><code>Right</code>: Gets rightmost characters</li>
</ul>
<h2 id="performance-notes">Performance Notes</h2>
<ul>
<li>Asc is a very fast operation (direct character code lookup)</li>
<li>More efficient than string comparison for single character checks</li>
<li>Use Asc for character-based validation instead of multiple string comparisons</li>
<li>In tight loops, cache Asc results if checking the same character repeatedly</li>
</ul>
<h2 id="parsing-notes">Parsing Notes</h2>
<p>The <code>Asc</code> function is not a reserved keyword in VB6. It is parsed as a regular
function call (<code>CallExpression</code>). This module exists primarily for documentation
purposes and to provide a comprehensive test suite that validates the parser
correctly handles <code>Asc</code> function calls in various contexts.</p>
</article>
<div style="margin-top: 3rem; padding-top: 2rem; border-top: 1px solid var(--border-color);">
<p>
<a href="index.html">← Back to String</a> |
<a href="../index.html">View all functions</a>
</p>
</div>
</main>
<footer>
<div class="container">
<p>© 2024-2026 VB6Parse Contributors. Licensed under the MIT License.</p>
</div>
</footer>
</body>
</html>