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C Program to Check Prime Number Using Efficient Logic

  Introduction A prime number is a number that has exactly two distinct positive divisors: 1 and itself. In this program, we check whether a given number is prime or not using a simple and efficient logic. This type of program is commonly used in mathematics, competitive programming, and basic algorithm learning for beginners in C programming. Problem Statement The task is to write a C program that determines whether a given integer is a prime number or not. The program takes a single integer input from the user and analyzes its divisibility. If the number has no divisors other than 1 and itself, it should be identified as a prime number; otherwise, it is not prime. This problem is important in number theory and has practical relevance in areas such as cryptography, data validation, and algorithm design.  Algorithm / Logic Explanation To check whether a number is prime, we need to verify that it is not divisible by any number other than 1 and itself. The algorithm follows a si...
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Print Prime Numbers up to a Limit in C

Prime Numbers from 1 to N in C

✅ C Program to Print Prime Numbers from 1 to N

#include <stdio.h>

int main() {
    int n, i, j, count;

    printf("Enter the ending value: ");
    scanf("%d", &n);

    printf("Prime numbers from 1 to %d are:\n", n);
    for(i = 2; i <= n; i++) {
        count = 0;
        for(j = 1; j <= i; j++) {
            if(i % j == 0) {
                count++;
            }
        }
        if(count == 2) {
            printf("%d ", i);
        }
    }

    return 0;
}

🧠 Explanation:

  • The program takes user input n and prints all prime numbers from 1 to n.
  • It checks each number i from 2 to n.
  • For each i, it counts how many numbers divide it (using variable count).
  • If a number has exactly 2 factors (1 and itself), it is prime and printed.

🖥️ Sample Output:

Enter the ending value: 15
Prime numbers from 1 to 15 are:
2 3 5 7 11 13

🔑 Keywords:

Prime number program in C, C program using nested loops, check prime in C, number logic programs, beginner-friendly C program, coding interview logic

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