{"id":747,"date":"2024-10-19T13:38:14","date_gmt":"2024-10-19T08:08:14","guid":{"rendered":"https:\/\/codexplained.in\/?p=747"},"modified":"2025-11-24T15:36:38","modified_gmt":"2025-11-24T10:06:38","slug":"check-prime-number","status":"publish","type":"post","link":"https:\/\/codexplained.in\/?p=747","title":{"rendered":"Check Prime Number"},"content":{"rendered":"
\n#include <stdio.h>\n\nint main() \n{\n    int number, i, isPrime = 1;\n\n    \/\/ Asking the user to input a number\n    printf("Enter an integer: ");\n    scanf("%d", &number);\n\n    \/\/ Prime numbers are greater than 1\n    if (number <= 1) {\n        isPrime = 0;\n    } else {\n        \/\/ Checking divisibility from 2 to number\/2\n        for (i = 2; i <= number \/ 2; i++) {\n            if (number % i == 0) {\n                isPrime = 0;\n                break; \/\/ If divisible, no need to check further\n            }\n        }\n    }\n\n    \/\/ Output whether the number is prime or not\n    if (isPrime == 1) {\n        printf("%d is a prime number.\\n", number);\n    } else {\n        printf("%d is not a prime number.\\n", number);\n    }\n\n    return 0;\n}\n\n<\/pre><\/div>\n\n\n
Explanation:<\/h3>\n\n\n\n
    \n
  1. Including the standard input-output library<\/strong>: We include the stdio.h<\/code> header file to use the printf<\/code> and scanf<\/code> functions for input and output.cCopy code#include <stdio.h><\/code><\/li>\n\n\n\n
  2. Main function<\/strong>: The execution of the program starts with the main()<\/code> function.cCopy codeint main() { ... }<\/code><\/li>\n\n\n\n
  3. Declaring variables<\/strong>:
    • number<\/code> is used to store the number input by the user.<\/li>
    • i<\/code> is used as a loop counter for checking divisibility.<\/li>
    • isPrime<\/code> is a flag variable. It starts as 1<\/code> (assuming the number is prime). If we find any divisor, we change it to 0<\/code> (not prime).<\/li><\/ul>cCopy codeint number, i, isPrime = 1;<\/code><\/li>\n\n\n\n
    • User input<\/strong>: We prompt the user to input a number using printf<\/code> and store it in the number<\/code> variable using scanf<\/code>.cCopy codeprintf(\"Enter an integer: \"); scanf(\"%d\", &number);<\/code><\/li>\n\n\n\n
    • Checking if the number is prime<\/strong>:
      • Prime numbers are greater than 1, so if the number is less than or equal to 1, we directly set isPrime = 0<\/code>.<\/li>
      • For numbers greater than 1, we check if the number is divisible by any integer from 2 to number\/2<\/code> (because a number cannot have any divisor greater than its half). If we find a divisor, we set isPrime = 0<\/code> and break the loop since the number is not prime.<\/li><\/ul>cCopy codeif (number <= 1) { isPrime = 0; } else { for (i = 2; i <= number \/ 2; i++) { if (number % i == 0) { isPrime = 0; break; } } }<\/code><\/li>\n\n\n\n
      • Displaying the result<\/strong>:
        • If isPrime<\/code> is still 1<\/code>, the number is prime, so we print a message saying it is a prime number.<\/li>
        • If isPrime<\/code> is 0<\/code>, we print that the number is not prime.<\/li><\/ul>cCopy codeif (isPrime == 1) { printf(\"%d is a prime number.\\n\", number); } else { printf(\"%d is not a prime number.\\n\", number); }<\/code><\/li>\n\n\n\n
        • Returning 0<\/strong>: The program returns 0<\/code> to indicate successful execution.cCopy codereturn <\/code>0<\/li>\n<\/ol>\n\n\n\n
          OUTPUT<\/h2>\n\n\n\n
          Enter an integer: 7
          7 is a prime number.<\/p>\n\n\n\n
          Summary:<\/h2>\n\n\n\n
          The program checks divisibility starting from 2 up to number\/2<\/code>. If any divisor is found, the number is not prime. Otherwise, it’s a prime number.<\/p>\n\n\n\n
          A prime number is a number greater than 1 that has no divisors other than 1 and itself.<\/p>\n