Is it prime? function 

	1. The method 
/*
Here isPrime function to test if the entered positive integer 
number is prime or not. The related algorithm is the following:


int isPrime(int x){
int i;
int is_prime=1;

for(i = 2; i <= x/2; i++){
if((x % i) == 0)
is_prime = 0;

}
return is_prime;
}

The integer 2 is prime. To test whether an integer "x" is prime, we 
calculate its modulo (x,n); n varies from 2 to x/2. Note that the 
division of x by the numbers between x/2 and x( x excluded) gives 
float numers between 2 and 1, then in this range, we have never 
mod(x,n) = 0. It is then reasonable to stop evaluating the 
modulo at x/2.


	2. Example in C language:


*/
#include 

int isPrime(int x){
int i;
int is_prime=1;

for(i = 2; i <= x/2; i++){
if((x % i) == 0)
is_prime = 0;

}
return is_prime;
}


int main()
{
float number;
float decimal_part;
int integer_part;

printf("\n Enter a positive integer: -->");
scanf("%f", &number);

integer_part= (int)number;
decimal_part = number - integer_part;

if(number <=0)
	printf("\n Enter a positive integer! \n");

else if(decimal_part !=0)
	printf("\n Enter an integer! \n");


else if(isPrime(integer_part) == 1)
printf("\n The entered number %d is prime.\n",integer_part);
else
printf("\n The entered number %d is not prime.\n",integer_part);



return 0;
}

3. Example in Fortran90 language:

LOGICAL FUNCTION is_it_prime(Number)
IMPLICIT NONE
INTEGER :: Number
INTEGER :: Div

IF (Number == 2) THEN
is_it_prime = .TRUE.
ELSE IF (MOD(Number, 2) == 0) THEN
is_it_prime = .FALSE.
ELSE
Div = 3
DO
IF (MOD(Number,Div)==0) EXIT
Div = Div + 2
END DO
is_it_prime = Div == NUMBER
! Divide untill Divisor = Number, to make sure that the integer is prime
END IF
END FUNCTION is_it_prime


! Main program
!-------------

PROGRAM is_prime
IMPLICIT NONE
INTEGER :: Number
LOGICAL :: is_it_prime
!Get an integer:
WRITE(*,*) "\n Enter an integer: -->  "
READ(*,*) Number
IF (is_it_prime(Number)) THEN
WRITE(*,*) "The number", Number , " is prime. \n"
else
WRITE(*,*) "The number", Number , " is not prime. \n"
END IF

END PROGRAM is_prime