PHP Program to Base Conversion with Validation with Explanation
PHP
Hard
PHP Error Handling
32 views
1 min read
90 words
This problem helps you practice core PHP fundamentals in a practical way. It builds intuition around base, invalid, decimal. Let’s break it down step by step so you can implement it confidently.
Problem Statement
Given base b and string s, convert to decimal. If s contains invalid digit for base, print INVALID.
Input Format
One line: b s.
Output Format
Decimal or INVALID.
Constraints
2
Code Solution
This explanation is written for learning purposes and to help beginners understand the concept clearly.
<?php
$inputText=trim(stream_get_contents(STDIN));
if($inputText==='') exit;
[$b,$s]=preg_split('/\\s+/', $inputText, 2);
$base=intval($b);
$s=strtoupper(trim($s));
$val=0;
for($i=0,$n=strlen($s);$i<$n;$i++){
$ch=$s[$i];
if($ch>='0' && $ch<='9') $d=ord($ch)-48;
elseif($ch>='A' && $ch<='Z') $d=ord($ch)-55;
else{ echo 'INVALID'; exit; }
if($d<0 || $d>=$base){ echo 'INVALID'; exit; }
$val=$val*$base + $d;
}
echo strval($val);
?>
Common Mistakes
- Misreading input/output format.
- Not handling constraints and edge cases.
- Off-by-one errors in loops.
- Forgetting to reset variables between test cases (if any).
Solution Guide
Problem
Given base b and string s, convert to decimal. If s contains invalid digit for base, print INVALID.
Input / Output
Output
Decimal or INVALID.
Details
Common Mistakes
- Misreading input/output format.
- Not handling constraints and edge cases.
- Off-by-one errors in loops.
- Forgetting to reset variables between test cases (if any).
Official Solution
<?php
$inputText=trim(stream_get_contents(STDIN));
if($inputText==='') exit;
[$b,$s]=preg_split('/\\s+/', $inputText, 2);
$base=intval($b);
$s=strtoupper(trim($s));
$val=0;
for($i=0,$n=strlen($s);$i<$n;$i++){
$ch=$s[$i];
if($ch>='0' && $ch<='9') $d=ord($ch)-48;
elseif($ch>='A' && $ch<='Z') $d=ord($ch)-55;
else{ echo 'INVALID'; exit; }
if($d<0 || $d>=$base){ echo 'INVALID'; exit; }
$val=$val*$base + $d;
}
echo strval($val);
?>
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