Prime Numbers Between Given Two Numbers

This C program is designed to find and print prime numbers within a specified range defined by two input numbers.

#include<stdio.h>
main()
{
  int num1,num2,i,count=0,j;
  printf("Enter a number 1\n");
  scanf("%d",&num1);
  printf("Enter a number 2\n");
  scanf("%d",&num2);
  printf("The Prime numbers between %d and %d are\n",num1,num2);
  for(i=num1;i<=num2;i++)
  {
    count=0;
    for(j=1;j<=i;j++)
    {
      if(i%j==0)
      {
        count++;
      }
    }
    if(count==2)
    {
      printf("%d\n",i);
    }
  }
}

Enter a number 1
2000
Enter a number 2
2100
The Prime numbers between 2000 and 2100 are
2003
2011
2017
2027
2029
2039
2053
2063
2069
2081
2083
2087
2089
2099

Let’s break down the code step by step:

1. Variable Declarations:

   int num1, num2, i, count = 0, j;

Here, the variables are declared to store the input numbers (num1 and num2), loop counters (i and j), and a counter (count) to determine the factors of each number.

2. User Input:

   printf("Enter a number 1\n");
   scanf("%d", &num1);
   printf("Enter a number 2\n");
   scanf("%d", &num2);

The program prompts the user to enter two integer numbers (num1 and num2), defining the range for finding prime numbers.

3. Prime Number Identification Loop:

   printf("The Prime numbers between %d and %d are\n", num1, num2);
   for (i = num1; i <= num2; i++) {

A for loop iterates through the numbers in the specified range.

4. Factor Counting Loop:

   count = 0;
   for (j = 1; j <= i; j++) {
       if (i % j == 0) {
           count++;
       }
   }

Nested within the outer loop, another for loop is used to count the number of factors of the current number (i). The count variable is reset to 0 for each iteration.

5. Prime Number Check:

   if (count == 2) {
       printf("%d\n", i);
   }

After counting the factors, if the count is exactly 2, it means the current number has only two factors (1 and itself), indicating that it is a prime number. In such cases, the prime number is printed.

6. Conclusion:
   The program prints all prime numbers within the specified range (num1 to num2) by checking the number of factors for each integer in that range. If a number has exactly two factors, it is considered prime, and the program prints it.