Write a C program to find prime number up to given integer.

Problem:  Write a function to find whether a given no. is prime or not. Use the same to generate the  prime numbers less than 100.

What is prime number: A prime number is a natural number greater than 1 that is not a product of two smaller natural numbers.A natural number greater than 1 that is not prime is called a composite number. for example,11 is prime because he only ways of writing it as a product,1* 5 or 5*1, involve 5 itself.

Source

Source Code:

/*******************************************/

1. #include <stdio.h>
2. #include<conio.h>
3.  
4. int main()
5.  {
6.                //variables declaration
7.     int i, j, n, isPrime;
8.  
9.     // Reads upper limit to print prime.
10.     printf("Enter number: ");
11.     scanf("%d", &n);
12.  
13.         printf("\n Prime numbers up to %d are: \n", n);
14.  
15.     // Finds all Prime numbers between 1 to n.
16.     for(i=2; i<=n; i++)
17.                 {
18.         // Assume that the current number is Prime.
19.         isPrime = 1;
20.  
21.         // Check if the current number i is prime or not.
22.         for(j=2; j<=i/2; j++)
23.                               {
24.            
25.             if(i%j==0)
26.                                              {
27.                 isPrime = 0;
28.                 break;
29.             }
30.         }
31.  
32.         /* If the number is prime then print */
33.         if(isPrime==1)
34.                               {
35.         //display the prime number.
36.             printf(" %d \t", i);
37.         }
38.     }
39.     getch();
40.    
41. }

Output:

Enter number: 35

 Prime numbers up to 35 are:

 2       3       5       7       11      13      17      19      23      29

 31

Enter number: 57

 Prime numbers up to 57 are:

 2       3       5       7       11      13      17      19      23      29

 31      37      41      43      47      53