PHP functions and their uses

PHP is a popular server-side programming language that has a wide range of applicability, ranging from simple web forms to large enterprise-level applications. As an open source programming language, PHP has many powerful functions that can complete a variety of tasks, from string processing to graphics processing to database access. In this article, we will explore some commonly used PHP functions and their uses.

1. String processing functions
PHP has many powerful functions in string processing. The following are several commonly used string processing functions and their uses:

1. strlen()
   Its function is to return the length of a given string.
2. strpos()
   Its function is to find the specified text in the string. It returns the position of the first occurrence of the string being searched for.
3. substr()
   Its function is to return the specified number of characters from the string.
4. str_replace()
   Its function is to search and replace the specified text in the string.
5. strtolower()
   Its function is to convert the string to lowercase.

2. Mathematical functions
PHP has many mathematical functions that can perform numerical calculations, such as:

1. ceil()
   its function is rounding to the nearest integer, rounded up.
2. floor()
   Its function is to round to the nearest integer and round down.
3. round()
   Its function is to round the value according to the rounding rules.
4. sqrt()
   Its function is to return the arithmetic square root of the number.
5. rand()
   Its function is to generate a random number.

3. File operation functions
PHP can read and write files. The following are several commonly used file operation functions and their uses:

1. fopen( )
   Its function is to open a file and return a file handle.
2. fread()
   Its function is to read the file.
3. fwrite()
   Its function is to write data to a file.
4. fclose()
   Its function is to close the open file.

4. Array functions
PHP arrays are commonly used data structures. The following are several commonly used array functions and their uses:

1. in_array()
   Its function is to find whether a certain value exists in the array.
2. array_push()
   Its function is to add one or more values ​​to the end of the array.
3. array_pop()
   Its function is to take out and return the last element from the array.
4. array_merge()
   Its function is to merge two or more arrays into one array.

5. Time and date functions
PHP has functions for processing time and date:

1. time()
   Its function is to return the current Unix time stamp.
2. mktime()
   Its function is to return the Unix timestamp of a date.
3. date()
   Its function is to format the Unix timestamp into a readable date.
4. strtotime()
   Its function is to convert any English text time to a Unix timestamp.

6. Database functions
PHP has the function of accessing the database. The following are several commonly used database functions and their uses:

1. mysqli_connect()
   Its function is to establish a connection with the MySQL database.
2. mysqli_query()
   Its function is to execute MySQL queries.
3. mysqli_fetch_array()
   Its function is to take a row from the result set as an associative array or numeric array.
4. mysqli_close()
   Its function is to close the mysqli connection.

Summary:
PHP has a rich function library for processing strings, values, files, arrays, time, dates, databases, etc. Being proficient in these functions will make writing PHP programs easier and more efficient. Of course, there are many functions that need to be learned and used as needed.

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