Pthread integral. To build enter command: > make

main.c

#include <sys/types.h>
#include <sys/stat.h>
#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <pthread.h>

int i, n;
// Max n = 10000
double a, b;
double result = 0.0, length;
double *from_this;

/*  Your function */
double f(double x) {
	return 1 / ( x * x );
}

/* Thread */
void *integrate(void *arg) {
	double local = *(double *)arg;
	double u;
	/* Middle of [a;b] */
	u = local + length/2; 
	result += f(u)*length;
	pthread_exit(NULL);
}

int main(int argc, char **argv) {
	if (argc != 4) {
		printf("Wrong numbers of parameters. USAGE: a b n\n");
		exit(-1);
	}

	a = atof(argv[1]);
	b = atof(argv[2]);
	n = atoi(argv[3]);

	/* Length division */
	length = ( b - a ) / n;

	pthread_t tid[n];

	from_this = ( double * ) malloc( n * sizeof( double ) );

	for ( i = 0; i < n; i++ ) {
		from_this[ i ] = a + i * length;
		if ( pthread_create(&tid[i], NULL, integrate, (void *) &from_this[i]) ) {
			printf("Error of creating thread: %s\n", strerror(errno));
			exit(-1);
		}
	}

	for ( i = 0; i < n; i++ ) {
		if ( pthread_join(tid[i], NULL) ) {
			printf("Error of joining thread %d: %s\n", i, strerror(errno));
			exit(-1);
		}
	}

	double out = result;

	printf("Integral equals to %lf.\n", out);

	free(from_this);

	return 0;
}

Makefile

CC=gcc
CFLAGS=-Wall -ggdb

all: Integral

Integral: main.c 
	$(CC) $(CFLAGS) -o integral main.c -lpthread