 # PHP Program to check whether the number is prime or composite

## What is a Prime Number & Composite Number?

Prime numbers are natural numbers that are greater than 1 that are not a product of two smaller natural numbers.  Prime numbers are natural numbers that are greater than 1 that are not a product of two smaller natural numbers. Composite numbers are natural numbers greater than 1 and which are not prime numbers. For example, 7 has no divisors other than 1 and 7 itself which is a prime number and   has more than two divisors which is a composite number.

## How to Check Whether the Number is Prime or Composite in PHP?

In PHP to check whether the number is Prime or Composite by using Mod(%) Operator. We have used a user-defined function to check the number and the user entered number will be passed as an argument and it first checks whether it is greater than 1 or not. If it is 1 it will directly return 0 or else check for whether the number can be perfectly divisible by other numbers less than the number itself by the operation (num % i == 0). If it is then it will return otherwise it will return 1 from the function check_num().

### ALGORITHM

Step 1: Accept the number into the variable num

Step 2: Create a variable flag to assign the return value from the `user-defined function` check_num() with argument num

Step 3: By using the if statement check the condition if the value of the variable flag is 1 if true print the 'It is a prime number' otherwise print 'It is a  composite number' using the function `echo`.

### ALGORITHM User define function : check_num(num)

Step 1: check for the num is 1 by using the `if` statement if true return 0 as the result of the `function` check_num() and exit otherwise perform the following steps.

Step 2: Perform the for loop and assign the value 2 into variable i and perform the sub-step until the condition 'i <= num / 2' becomes false and increment the value of variable i in every iteration

(i) check the condition 'num % i == 0' it true return 0 as the result of the `function` check_num()

Step 3: return 1 as the result of the `function` check_num()

## PHP Source Code

```                                          ```<?php
function check_num(\$num)
{
if (\$num == 1)
return 0;
for (\$i = 2; \$i <= \$num / 2; \$i++) {
if (\$num % \$i == 0)
return 0;
}
return 1;
}
\$num = readline("Enter the number: ");
\$flag = check_num(\$num);
if (\$flag == 1)
echo "It is a prime number";
else
echo "It is a composite number";
?>```
```

## OUTPUT

```Example 1
Enter the number: 1
It is a composite number

Example 2
Enter the number: 79
It is a prime number

Example 3
Enter the number: 56
It is a composite number```
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