c - 计算阶乘时的长格式处理

Question

我编写了一段代码，在创建 myFactorial 函数后计算阶乘，但是当我尝试处理更大的数字时，我把它搞砸了。

我正在尝试使用长格式处理 16 以上的数字，但结果无关紧要，并且代码的第二部分事情变得更奇怪。 虽然结果不应随输入而改变，但它们确实会改变!

我通过下面的评论分享我的代码:

main.c

#include <stdio.h>
#include <stdlib.h>


int main()
{
    int yourNumber;
    int i;

    //Take the input
    printf("I highly recommend you to make the command window fullscreen. Otherwise, the complete output will not be seen.\n");
    printf("Enter a positive integer and I will tell you its factorial.\n");
    scanf("%d", &yourNumber);

    //Calculate factorial and print it in three ways
    printf("Factorial of %d is %d!\n",yourNumber,myFactorial(yourNumber));
    printf("Using long format, factorial of %d is %lld!\n",yourNumber,myFactorial(yourNumber));
    printf("In hex: %#08X!",myFactorial(yourNumber));




    // Here on, second part of my code begins


    // Calculate and print factorials of numbers from 1 to 20 in %d format
    printf("\n\n\nLet's see more d's!\n\n");
    for (i = 1; i<21; i++)   printf("%d\n", myFactorial(i));

    // Calculate and print factorials of numbers from 1 to 20 in %lld format
    printf("\n\n\nNow let's see more lld's!\n\n");
    for (i = 1; i<21; i++)   printf("%lld\n", myFactorial(i));


    return 0;
}

---

myfactorial.c

#include <stdio.h>

long long int myFactorial(int bar) {
    long long out = 1;
    int i;
    for (i=1; i<=bar; i++)
    {
        out *= i;
    }
    return out;
}

Answer 1

您的 printf 有问题格式:

全部printf打印 myFactorial 的返回值必须使用 %lld格式，为long long int

printf打印十六进制值必须使用 %llX打印正确的值

//Calculate factorial and print it in three ways
printf("Factorial of %d is %lld!\n",yourNumber,myFactorial(yourNumber));
printf("Using long format, factorial of %d is %lld!\n",yourNumber,myFactorial(yourNumber));
printf("In hex: %#016llX!",myFactorial(yourNumber));

// Here on, second part of my code begins

// Calculate and print factorials of numbers from 1 to 20 in %d format
printf("\n\n\nLet's see more d's!\n\n");
for (i = 1; i<21; i++)   printf("%lld\n", myFactorial(i));

// Calculate and print factorials of numbers from 1 to 20 in %lld format
printf("\n\n\nNow let's see more lld's!\n\n");
for (i = 1; i<21; i++)   printf("%lld\n", myFactorial(i));

您只需添加 -Wall 即可找到此类错误使用 gcc 编译时的选项。它会告诉你

test.c: In function ‘main’:
test.c:84:5: warning: format ‘%d’ expects argument of type ‘int’, but argument 3 has type ‘long long int’ [-Wformat=]
     printf("Factorial of %d is %d!\n",yourNumber,myFactorial(yourNumber));
     ^
test.c:86:5: warning: format ‘%X’ expects argument of type ‘unsigned int’, but argument 2 has type ‘long long int’ [-Wformat=]
     printf("In hex: %#08X!",myFactorial(yourNumber));
     ^
test.c:94:5: warning: format ‘%d’ expects argument of type ‘int’, but argument 2 has type ‘long long int’ [-Wformat=]
     for (i = 1; i<21; i++)   printf("%d\n", myFactorial(i));

最好添加以下所有选项:-Wall -Wextra -pedantic

Take note that your code can work correctly as far as the factorial is less then 9223372036854775807 that is the maximum allowed for long long int

这意味着您可以计算阶乘，其中 x <= 20