如何删除 C 程序中输出的第一个 *？

Question

我正在尝试编写一个程序来打印给定数字的质因数，但我需要将它们以 * 分隔打印，例如：对于输入 100，输出将是：2 *2*5*5，有什么建议吗？到目前为止我这样做了：

# include <stdio.h> 
# include <math.h> 

void decomposicao(int n) 
{ 
    printf("%d = ", n);

    while (n%2 == 0) 
    { 
        n = n/2;
        printf("* %d ", 2); 
    } 

    for (int i = 3; i <= sqrt(n); i = i+2) 
    { 
        while (n%i == 0) 
        { 
            n = n/i; 
            printf("* %d ", i);     
        } 
    } 

    if (n > 2) 
        printf ("* %d ", n); 

} 
int main() 
{ 
    int n;

    scanf("%d", &n);

    if (n<=0||n==1)     
    {   
        printf("Error", n);
    }
    else
    {
        decomposicao(n);
    }   

    return 0; 
}

对于此代码，输出为：

100 = *2*2*5*5

Answer 1

添加一个布尔变量，告诉您是否打印第一个因素。

#include <stdbool.h>

void decomposicao(int n) 
{ 
    bool first = true;
    printf("%d = ", n);

    while (n%2 == 0) 
    { 
        n = n/2;
        if (!first)
            printf("* ");

        printf("%d ", 2); 
        first = false;
    } 

    for (int i = 3; i <= sqrt(n); i = i+2) 
    { 
        while (n%i == 0) 
        { 
            n = n/i; 
            if (!first)
                printf("* ");

            printf("%d ", i);
            first = false;  
        } 
    } 

    if (n > 2) {
        if (!first)
            printf("* ");

        printf ("%d ", n); 
    }
}

Answer 2

首先，您可以更改 * 的打印方式。而不是在你的字符串的乞求，只是把它放在最后。

现在，您可以写入内部缓冲区，而不是直接将结果写入输出流，完成后，只需忽略其中的最后两个字符即可。

void decomposicao(int n) 
{ 
    const size_t len = 512;
    char buffer[len];
    size_t written = 0;

    written = snprintf(buffer, len, "%d = ", n);

    while (n%2 == 0) 
    { 
        n = n/2;
        written += snprintf(buffer + written, len - written, "%d * ", 2); 
    } 

    for (int i = 3; i <= sqrt(n); i = i+2) 
    { 
        while (n%i == 0) 
        { 
            n = n/i; 
            written += snprintf(buffer + written, len - written, "%d * ", i);     
        } 
    } 

    if (n > 2) 
        written += snprintf(buffer + written, len - written, "%d * ", n); 

    buffer[len - 1] = '[=10=]';
    buffer[written - 2] = '[=10=]';
    printf("%s\n", buffer);

}

如何删除 C 程序中输出的第一个 *？

How to remove the first * of my output in a C program?

c

prime-factoring