Question

I need Help PLZ. I can't solving this in C program
Given is a C program count_primes.c, which is an array Generates 10000 six-digit random numbers and then determines the number of primes in that array. It also measures the time that elapses during the calculation and returns it to the console along with the number of primes it finds.

(a) Rewrite the program so that N threads are used to count the primes in the array. Each thread is supposed to check a separate part of the array (eg in case of two threads half each).

The number of threads should be passed as a program argument and not be firmly coded! Here is the maximum possible value for
N up10 be limited.

Note: Use POSIX threads. Include the header <pthread.h>. Also, when calling gcc, you must specify -pthread as an additional option. B .: gcc -o count_primescount_primes.c-g-pthread
(b) Test your program for N = 1,2,4 and 8 threads and graph the results.
Explain briefly what value the runtime is for very large N is expected to converge.
In addition, briefly describe a negative effect that you can get with very large ones N gets.

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <sys/time.h> // Include for use time functions
#include <pthread.h> // Include for POSIX threads

/** Return milliseconds elapsed since given time. */
int getElapsedTime(struct timeval startTime)
{
struct timeval stopTime, elapsedTime;
gettimeofday(&stopTime, NULL);
timersub(&stopTime, &startTime, &elapsedTime);
return 1000*elapsedTime.tv_sec + elapsedTime.tv_usec/1000;
}

/** Return true if given number z is a prime number. */
bool isPrime(int z)
{
int t = 2;
int tmax = z / 2;
while (t <= tmax && z % t != 0) {
t++;
}
return t > tmax;
}

/**
* Main program: Check n integer values for primes.
*/
int main(int argc, char* argv[])
{
// Create n random integers in array
int numValues = 10000;
int values[numValues];
for (int i = 0; i < numValues; i++) {
values[i] = rand() % 900000 + 100000;
}

// Get current time for time measurement
struct timeval startTime;
gettimeofday(&startTime, NULL);

// Check array for primes in main thread
// TODO: Distribute this to m threads!
int numPrimes = 0;
for (int i = 0; i < numValues; i++) {
if (isPrime(values[i])) {
numPrimes++;
}
}

// Measure computation time
int msec = getElapsedTime(startTime);

// Display results
printf("Found %d primes in %d values in %d ms\n",
       numPrimes, numValues, msec);

return 0;
}

Answer 1

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <sys/time.h> // Include for use time functions
#include <pthread.h> // Include for POSIX threads

struct arguments
{
   int * array;
   int num;
   int noPrimes;
};
/** Return milliseconds elapsed since given time. */
int getElapsedTime(struct timeval startTime)
{
struct timeval stopTime, elapsedTime;
gettimeofday(&stopTime, NULL);
timersub(&stopTime, &startTime, &elapsedTime);
return 1000*elapsedTime.tv_sec + elapsedTime.tv_usec/1000;
}

/** Return true if given number z is a prime number. */
bool isPrime(int z)
{
int t = 2;
int tmax = z / 2;
while (t <= tmax && z % t != 0) {
t++;
}
return t > tmax;
}
/** function to find number of primes in given array
*/
void *numOfPrimes(void * args)
{
   struct arguments * arg = (struct arguments *) args;
   int *values=arg->array;
   int numValues=arg->num;
   int numPrimes = 0;
for (int i = 0; i < numValues; i++) {
if (isPrime(values[i])) {
numPrimes++;
   arg->noPrimes=numPrimes;
}
}
}
/**
* Main program: Check n integer values for primes.
*/
int main(int argc, char* argv[])
{
// Create n random integers in array
int numValues = 10000;
int values[numValues];
for (int i = 0; i < numValues; i++) {
values[i] = rand() % 900000 + 100000;
}
// Get current time for time measurement
struct timeval startTime;
gettimeofday(&startTime, NULL);
int N;
printf("enter number of threds you need to add\n");
scanf("%d",&N);
pthread_t thread[N]; //thread array to store N number of threads
struct arguments *args[N];
for(int i=0;i<N;i++){
   args[i]=(struct arguments *)malloc (sizeof (struct arguments));
   args[i]->array=&values[0]+i*N; //divide array into N parts
   args[i]->num=numValues/N;
args[i]->noPrimes=0;   //to store number of primes from each thread
   pthread_create(& thread[i], NULL, numOfPrimes,args[i]);
}  
for(int i=0;i<N;i++)
{
   pthread_join(thread[i],NULL); //wait till all the threds finish their job before main going to terminate them
}
// Measure computation time
int msec = getElapsedTime(startTime);
int numPrimes=0;
for(int i=0;i<N;i++)
{
   numPrimes+=args[i]->noPrimes;
}
// Display results
printf("Found %d primes in %d values in %d ms\n",
numPrimes, numValues, msec);

return 0;
}