Question

C Program only - MUST USE MALLOC IN CODE

Research and implement the Sieve of Eratosthenes.

Example Program Session (implement some linefeed ‘\n’ formatting):

Enter the limit: 1000
Primes up to 1000

   2    3    5    7   11   13   17   19   23   29   31   37   41   43   47   53
59   61   67   71   73   79   83   89   97 101 103 107 109 113 127 131
137 139 149 151 157 163 167 173 179 181 191 193 197 199 211 223
227 229 233 239 241 251 257 263 269 271 277 281 283 293 307 311
313 317 331 337 347 349 353 359 367 373 379 383 389 397 401 409
419 421 431 433 439 443 449 457 461 463 467 479 487 491 499 503
509 521 523 541 547 557 563 569 571 577 587 593 599 601 607 613
617 619 631 641 643 647 653 659 661 673 677 683 691 701 709 719
727 733 739 743 751 757 761 769 773 787 797 809 811 821 823 827
829 839 853 857 859 863 877 881 883 887 907 911 919 929 937 941
947 953 967 971 977 983 991 997

Number of primes: 168

Press any key to continue . . .

Answer 1

Code:

#include <stdio.h>
#include <stdlib.h>
int main(){
int i,j,LIMIT,count=0;
int *primes;
printf("Enter the limit: ");
scanf("%d",&LIMIT); //take limit from user
primes = malloc(sizeof(int)*LIMIT); //create array using malloc
//fill the array with 1
for (i=2;i<=LIMIT;i++)
primes[i]=1;
//sieve the non-primes and then put 0s on all the numbers that are not primes
for (i=2;i<=LIMIT;i++)
if (primes[i])
for (j=i;i*j<=LIMIT;j++)
primes[i*j]=0;
//print the numbers that are prime
printf("Primes up to %d\n",LIMIT);
for (i=2;i<=LIMIT;i++)
if (primes[i])
{
count++;
printf("%d\t",i);
}
printf("\nNumber of primes= %d",count);
return 0;
}

Output: