{"id":765,"date":"2024-10-19T13:35:18","date_gmt":"2024-10-19T08:05:18","guid":{"rendered":"https:\/\/codexplained.in\/?p=765"},"modified":"2025-11-24T15:36:55","modified_gmt":"2025-11-24T10:06:55","slug":"find-factorial-of-a-number","status":"publish","type":"post","link":"https:\/\/codexplained.in\/?p=765","title":{"rendered":"Find Factorial of a Number"},"content":{"rendered":"
\n#include <stdio.h>\n\nint main() {\n    int number, i;\n    unsigned long long factorial = 1;  \/\/ Use unsigned long long for large results\n\n    \/\/ Asking the user to input a positive integer\n    printf("Enter a positive integer: ");\n    scanf("%d", &number);\n\n    \/\/ Factorial of negative numbers doesn't exist\n    if (number < 0) {\n        printf("Factorial of a negative number doesn't exist.\\n");\n    } else {\n        \/\/ Calculating factorial\n        for (i = 1; i <= number; ++i) {\n            factorial *= i;  \/\/ Multiply factorial by i\n        }\n        \/\/ Output the result\n        printf("Factorial of %d = %llu\\n", number, factorial);\n    }\n\n    return 0;\n}\n\n<\/pre><\/div>\n\n\n
Explanation:<\/h2>\n\n\n\n
Returning 0<\/strong>: The program returns 0<\/code> to indicate successful execution.cCopy codereturn 0;<\/code><\/p>\n\n\n\n
Including the standard input-output library<\/strong>: We include the stdio.h<\/code> header file so we can use printf<\/code> for output and scanf<\/code> for input.cCopy code#include <stdio.h><\/code><\/p>\n\n\n\n
Main function<\/strong>: The program execution begins with the main()<\/code> function.cCopy codeint main() { ... }<\/code><\/p>\n\n\n\n
Declaring variables<\/strong>:
  • number<\/code> stores the input number.<\/li>
  • i<\/code> is the loop counter used to calculate the factorial.<\/li>
  • factorial<\/code> is initialized to 1 and is used to store the result of the factorial calculation. We use unsigned long long<\/code> because the factorial of larger numbers can get very large quickly.<\/li><\/ul>cCopy codeint number, i; unsigned long long factorial = 1;<\/code><\/p>\n\n\n\n
    User input<\/strong>: We prompt the user to input a positive integer using printf<\/code>, and scanf<\/code> stores the number in the number<\/code> variable.cCopy codeprintf(\"Enter a positive integer: \"); scanf(\"%d\", &number);<\/code><\/p>\n\n\n\n
    Checking for negative input<\/strong>: Factorial is not defined for negative numbers. If the user inputs a negative number, the program prints an error message.cCopy codeif (number < 0) { printf(\"Factorial of a negative number doesn't exist.\\n\"); }<\/code><\/p>\n\n\n\n
    Calculating the factorial<\/strong>:
    • If the input is a positive number or zero (because the factorial of 0 is 1), the program uses a for<\/code> loop to multiply numbers from 1 to the input number<\/code>.<\/li>
    • For example, if the user enters 5<\/code>, the loop will perform: 1 * 2 * 3 * 4 * 5<\/code>, and store the result in factorial<\/code>.<\/li><\/ul>cCopy codefor (i = 1; i <= number; ++i) { factorial *= i; }<\/code><\/p>\n\n\n\n
      Displaying the result<\/strong>: After calculating the factorial, the program prints the result using printf<\/code>. The format specifier %llu<\/code> is used to print an unsigned long long<\/code> integer.cCopy codeprintf(\"Factorial of %d = %llu\\n\", number, factorial);<\/code><\/p>\n\n\n\n
      OUTPUT<\/h2>\n\n\n\n
      Enter a positive integer: 5
      Factorial of 5 = 120<\/p>\n\n\n\n
      Enter a positive integer: 0
      Factorial of 0 = 1<\/p>\n\n\n\n
      Enter a positive integer: -3
      Factorial of a negative number doesn’t exist.<\/p>\n\n\n\n
      Summary:<\/h2>\n\n\n\n
      This program checks for negative input, calculates the factorial using a loop, and handles large numbers using unsigned long long<\/code>.<\/p>\n\n\n\n
      The factorial of a number is the product of all positive integers from 1 to that number.<\/p>\n\n\n\n
      For example, the factorial of 5<\/code> is 5! = 5 * 4 * 3 * 2 * 1 = 120<\/code>.<\/p>\n