String search functions (strpos, strstr) in PHP - Mini Project: Build & Apply

String Search Functions with strpos and strstr in PHP

📖 Scenario: You are building a simple text analyzer tool that helps users find specific words or phrases inside a paragraph. This tool will help users quickly locate where a word appears and extract parts of the text starting from that word.

🎯 Goal: Build a PHP script that uses strpos to find the position of a word in a sentence and strstr to extract the part of the sentence starting from that word.

📋 What You'll Learn

Create a string variable with a fixed sentence.

Create a variable holding the word to search for.

Use strpos to find the position of the word in the sentence.

Use strstr to get the part of the sentence starting from the word.

Print the position and the extracted substring.

💡 Why This Matters

🌍 Real World

Searching text is common in many applications like search engines, text editors, and data processing tools.

💼 Career

Understanding string search functions helps in web development, data parsing, and building user-friendly search features.

1

Create the sentence string

Create a string variable called sentence and set it to the exact value: "Learning PHP string functions is fun and useful."

PHP

# Create a string variable called sentence with the given text
# Your code here

Hint

Use double quotes to create the string exactly as shown.

2

Set the word to search for

Create a string variable called searchWord and set it to the exact value: "string"

PHP

<?php
$sentence = "Learning PHP string functions is fun and useful.";
# Create a string variable called searchWord with the value "string"
# Your code here

Hint

Remember to use double quotes for the string.

3

Find the position and extract substring

Use strpos with variables sentence and searchWord to find the position of searchWord in sentence and store it in a variable called position. Then use strstr with sentence and searchWord to get the substring starting from searchWord and store it in a variable called substring.

PHP

<?php
$sentence = "Learning PHP string functions is fun and useful.";
$searchWord = "string";
# Use strpos to find the position of searchWord in sentence and save to position
# Use strstr to get substring from searchWord in sentence and save to substring
# Your code here

Hint

Use the exact variable names and function calls as shown.

4

Print the results

Print the position stored in position using echo with the exact text: "Position: " followed by the position. Then print the substring stored in substring with the exact text: "Substring: " followed by the substring. Each print should be on its own line.

PHP

<?php
$sentence = "Learning PHP string functions is fun and useful.";
$searchWord = "string";
$position = strpos($sentence, $searchWord);
$substring = strstr($sentence, $searchWord);
# Print the position with the text "Position: "
# Print the substring with the text "Substring: "
# Your code here

Hint

Use echo and concatenate strings with .. Use \n for new lines.

Practice

1. What does the PHP function strpos do?

easy

A. Converts a string to uppercase

B. Extracts a substring starting from a specific character

C. Finds the position of a substring inside a string

D. Replaces a substring with another string

Solution

1. Step 1: Understand the purpose of strpos

   The strpos function searches for the first occurrence of a substring inside another string and returns its position.

2. Step 2: Compare with other options

   Options A, B, and C describe different string functions like strtoupper, strstr, and str_replace, which are not what strpos does.

3. Final Answer:

   Finds the position of a substring inside a string -> Option C

4. Quick Check:

   strpos = position finder [OK]

Hint: strpos returns position index of substring [OK]

Common Mistakes:

• Confusing strpos with strstr
• Thinking strpos extracts substring
• Assuming strpos replaces text

2. Which of the following is the correct syntax to find the position of 'cat' in the string $text = 'concatenate' using strpos?

easy

A. strpos('concatenate', 'cat')

B. strpos($text)

C. strpos('cat', $text)

D. strpos($text, 'cat')

Solution

1. Step 1: Identify correct parameter order for strpos

   The first parameter is the full string, the second is the substring to find. So strpos($text, 'cat') is correct.

2. Step 2: Check other options for errors

   strpos('concatenate', 'cat') uses a string literal instead of the variable. strpos('cat', $text) reverses parameters. strpos($text) misses the second parameter.

3. Final Answer:

   strpos($text, 'cat') -> Option D

4. Quick Check:

   strpos(string, substring) [OK]

Hint: First argument is full string, second is substring [OK]

Common Mistakes:

• Swapping the order of parameters
• Omitting the substring argument
• Passing substring as first argument

3. What will be the output of this PHP code?

$text = 'hello world';
$pos = strpos($text, 'world');
echo $pos;

medium

A. 6

B. 5

C. 0

D. false

Solution

1. Step 1: Find the position of 'world' in 'hello world'

   The string 'hello world' has 'world' starting at index 6 (counting from 0).

2. Step 2: Understand what strpos returns

   strpos returns the starting position of the substring, so it returns 6.

3. Final Answer:

   6 -> Option A

4. Quick Check:

   Position of 'world' in 'hello world' = 6 [OK]

Hint: Count characters from zero to substring start [OK]

Common Mistakes:

• Counting from 1 instead of 0
• Confusing position with length
• Expecting boolean true instead of position

4. The following code is intended to check if the word 'apple' exists in $fruit. What is the error?

$fruit = 'pineapple';
if (strpos($fruit, 'apple')) {
  echo 'Found';
} else {
  echo 'Not found';
}

medium

A. strpos returns false if found, so condition is wrong

B. strpos returns 0 for 'apple' position, which is treated as false

C. Missing third parameter in strpos

D. Syntax error in if statement

Solution

1. Step 1: Understand strpos return values

   strpos returns 0 if the substring is found at the start (index 0). In PHP, 0 is treated as false in conditions.

2. Step 2: Analyze the if condition behavior

   The condition if (strpos(...)) fails when strpos returns 0, so it wrongly goes to else.

3. Final Answer:

   strpos returns 0 for 'apple' position, which is treated as false -> Option B

4. Quick Check:

   Check strpos !== false to avoid 0 as false [OK]

Hint: Check strpos !== false, not just if() [OK]

Common Mistakes:

• Using if(strpos()) without strict false check
• Assuming strpos returns boolean true/false only
• Ignoring 0 as valid position

5. Given the string $sentence = 'The quick brown fox jumps', which code snippet correctly extracts the substring starting from the word 'brown' using strstr?

hard

A. echo strstr($sentence, 'brown');

B. echo strstr($sentence, 'brown', true);

C. echo strpos($sentence, 'brown');

D. echo substr($sentence, strpos($sentence, 'brown'));

Solution

1. Step 1: Understand strstr behavior

   strstr returns the part of the string starting from the first occurrence of the substring, including it.

2. Step 2: Analyze options

   echo strstr($sentence, 'brown'); correctly uses strstr to get substring from 'brown'. echo strstr($sentence, 'brown', true); returns part before 'brown'. echo strpos($sentence, 'brown'); returns position, not substring. echo substr($sentence, strpos($sentence, 'brown')); uses substr with strpos, which also works but is not strstr.

3. Final Answer:

   echo strstr($sentence, 'brown'); -> Option A

4. Quick Check:

   strstr returns substring from needle [OK]

Hint: strstr returns substring from needle, true returns before [OK]

Common Mistakes:

• Using third parameter true to get substring after needle
• Confusing strpos with strstr
• Expecting strpos to return substring