Prime number program in c using for loop

Prime number program in C

• A prime number is a whole number greater than 1 whose only factors are 1 and itself. A factor is a whole number that can be divided evenly into another number. The first few prime numbers are 2, 3, 5, 7, 11, 13, 17, 19, 23 and 29. 
• Numbers that have more than two factors are called composite numbers.

#1:  Prime number program in c using for loop

1. #include <stdio.h>
2. void main()
3. {
4.   int n1, n2,j, flag;
5.   long int  i;
6.   printf("Enter First  numbers(intevals): ");
7.   scanf("%d", &n1);
8.   printf("Enter Second  numbers(intevals): ");
9.   scanf("%d", &n2);
10.   printf("Prime numbers between %d and %d are: ", n1, n2);
11.   for(i=n1+1; i<n2; ++i)
12.   {
13.       flag=0;
14.       for(j=2; j<=i/2; ++j)
15.       {
16.         if(i%j==0)
17.         {
18.           flag=1;
19.           break;
20.         }
21.       }
22.       if(flag==0)
23.         printf("%ld ",i);
24.   }
25. }

Output:

1. Enter First  numbers(intevals): 1
2. Enter Second  numbers(intevals): 500
3. Prime numbers between 1 and 500 are: 2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67
4. 71 73 79 83 89 97 101 103 107
5. 109 113 127 131 137 139 149 151 157 163 167 173 179 181 191 193 197 199 211 223 227 229
6. 233 239 241 251 257 263 269 271
7. 277 281 283 293 307 311 313 317 331 337 347 349 353 359 367 373 379 383 389 397 401 409
8. 419 421 431 433 439 443 449 457
9. 461 463 467 479 487 491 499
10. Process returned 500 (0x1F4)   execution time : 4.833 s
11. Press any key to continue.