### C Program 4–To check whether a given number is prime or not

A prime number can be divided by 1 and itself, there are no other divisors,

Examples are : 2 3, 5, 7, 11, …..

To find out whether a given number is prime or not, here is the logic

1. Get the number

2. divide the given number from 2 to n-1 (Example if 6 is the number divided by 2,3,4,5 will get the remainder respectively 0,0,2,3)

3. increment a counter to 1 if the remainder is 0

4. if there counter variable is 0, then the given number is prime (because we didn’t get any remainder) else non prime

Here is the program

#include <stdio.h>
#include <conio.h>

int main()
{
int a,i,count=0;
printf("enter a"); //Let the given number is a
scanf("%d",&a); //get the number
for(i=2;i<a;i++) //divide the number a from 2 to a-1
{
if(a%i==0)
count++; //increment a counter if the divisibility is 0
}
if(count !=0) //if the counter is not zero, then prime
printf("a is not a prime number");
else
printf("a is a prime number");
getch();
return 0;
}

1. Sir ,
for ( i=2 ; i < math.pow(a,0.5) ; i++ ) will satisfy . Its enough if we iterate till the square root of the number .

2. problem s=1+12+123+1234+............+123....n terms

3. s=(1+2)/(1x2)+(1+2+3)/(1x2x3+)+.......+(1+2+3+......n terms)/(1x2x3x..........n terms)

4. s=1x2x3x4+2x3x4x5+3x4x5x6+4x5x6x7+5x6x7x8

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A system call is used by application or user programs to request service from the operating systems. Since the user programs does not have direct access to the kernel whereas the OS has the direct access. OS can access the hardware through system calls only. The following files has to be modified for implementing a system call /usr/src/linux-2.6.32.5/arch/x86/kernel/syscall_table_32.S /usr/src/linux-2.6.32.5/arch/x86/include/asm/unistd_32.h /usr/src/linux-2.6.32.5/include/linux/syscalls.h /usr/src/linux-2.6.32.5/Makefile New set of files to be created Create a new directory newcall/ inside the path “ /usr/src/linux-2.6.32.5/ ” Create new files Makefile, newcall.c and put them in the /usr/src/linux-2.6.32.5/newcall/ folder Create new user files (in any folder of Linux) to test the system call testnewcall.c, testnewcall.h (created in /home/pradeepkumar ) syscall_table_32.S Find the file /usr/src/linux-2.6.32.5/arch/x86/kernel/syscall_tab

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