构造不能存储数据

2013-09-12

结构不能存储数据#include stdio.h#include string.h#define MAXBKS 100#define MAXAUTL 40#define MA

结构不能存储数据


#include <stdio.h>
#include <string.h>

#define MAXBKS 100
#define MAXAUTL 40
#define MAXTITL 40

struct book {
    char title[MAXTITL];
    char author[MAXAUTL];
    float value;
};

int main(void)
{
    struct book library[MAXBKS];
    int count=0, index;

    printf("Please enter the book title, press [enter] at the start"
        " of a line to stop.\n");
    while(fgets(library[count].title, MAXTITL-1, stdin)!= NULL
            && library[count].title[0] != '\n' && count<MAXBKS){
        library[count].title[strlen(library[count].title)-1] = '\0';
        printf("Now, enter the author: ");
        fgets(library[count].author, MAXAUTL-1, stdin);
        library[count].author[strlen(library[count].author)-1] = '\0';
        printf("Now, enter the value: ");
        scanf("%f", &library[count++].value);
        if(getchar() == '\n') 
            ; 
        printf("Now, enter the title: ");
    }
    if(count > 0){
        printf("Here is the list of your books: \n");
        for(index=0; index<count; index++);
            printf("%s by %s: $%.2f.\n", library[index].title,
                library[index].author, library[index].value);
    }
    else
        printf("No books? So bad...\nBye Bye!\n");

    return 0;
}

引用

Please enter the book title, press [enter] at the start of a line to stop.

The C programming
Now, enter the author: K&R
Now, enter the value: 68
Now, enter the title:
Here is the list of your books:

by : $0.00.
Please enter the book title, press [enter] at the start of a line to stop.

No books? So bad...
Bye Bye!

这是我之前写的同样功能的代码，是我预想的结果。可是找不到两段代码的差异


int main(void)
{
    struct book library[MAXBKS];
    int count=0, index;

    printf("Please enter the book title. Please ENTER at the start of"
        " line to quit.\n");
    while(fgets(library[count].title, MAXTITL-1, stdin) != NULL
            && library[count].title[0] != '\n' && count<MAXBKS){
        library[count].title[strlen(library[count].title)-1] = '\0';
        printf("Now enter the author: ");
        fgets(library[count].author, MAXAUTL-1, stdin);
        library[count].author[strlen(library[count].author)-1] = '\0';
        printf("Now enter the value: ");
        scanf("%f", &library[count++].value);
        if(getchar() == '\n')
            ;
        printf("Enter the next title: ");
    }
    if(count > 0){
        printf("Here is the list of your books: \n");
        for(index=0; index<count; index++)
            printf("%s by %s: $%.2f.\n", library[index].title,
                library[index].author, library[index].value);
    }
    else
        printf("No books? Too bad.\n");

    return 0; 
 
}

引用

Please enter the book title. Please ENTER at the start of line to quit.
The C programming
Now enter the author: K&R
Now enter the value: 68
Enter the next title: ABC
Now enter the author: Edf
Now enter the value: 12
Enter the next title:
Here is the list of your books:
The C programming by K&R: $68.00.
ABC by Edf: $12.00.
Please enter the book title. Please ENTER at the start of line to quit.

No books? Too bad.

请各位大侠指教了，谢谢结构
[解决办法]
数据有存进去，原因在于
for(index=0; index<count; index++);
for循环后面多了一个分号，应该是笔误吧。

引用:


#include <stdio.h>
#include <string.h>

#define MAXBKS 100
#define MAXAUTL 40
#define MAXTITL 40

struct book {
    char title[MAXTITL];
    char author[MAXAUTL];
    float value;
};

int main(void)
{
    struct book library[MAXBKS];
    int count=0, index;

    printf("Please enter the book title, press [enter] at the start"
        " of a line to stop.\n");
    while(fgets(library[count].title, MAXTITL-1, stdin)!= NULL
            && library[count].title[0] != '\n' && count<MAXBKS){
        library[count].title[strlen(library[count].title)-1] = '\0';
        printf("Now, enter the author: "); 
 
        fgets(library[count].author, MAXAUTL-1, stdin);
        library[count].author[strlen(library[count].author)-1] = '\0';
        printf("Now, enter the value: ");
        scanf("%f", &library[count++].value);
        if(getchar() == '\n') 
            ; 
        printf("Now, enter the title: ");
    }
    if(count > 0){
        printf("Here is the list of your books: \n");
        for(index=0; index<count; index++);
            printf("%s by %s: $%.2f.\n", library[index].title,
                library[index].author, library[index].value);
    }
    else
        printf("No books? So bad...\nBye Bye!\n");

    return 0;
}

引用

Please enter the book title, press [enter] at the start of a line to stop.
The C programming
Now, enter the author: K&R
Now, enter the value: 68
Now, enter the title:
Here is the list of your books:

by : $0.00.
Please enter the book title, press [enter] at the start of a line to stop.

No books? So bad...
Bye Bye!

这是我之前写的同样功能的代码，是我预想的结果。可是找不到两段代码的差异


int main(void)
{
    struct book library[MAXBKS];
    int count=0, index;

    printf("Please enter the book title. Please ENTER at the start of"
        " line to quit.\n");
    while(fgets(library[count].title, MAXTITL-1, stdin) != NULL
            && library[count].title[0] != '\n' && count<MAXBKS){ 
 
        library[count].title[strlen(library[count].title)-1] = '\0';
        printf("Now enter the author: ");
        fgets(library[count].author, MAXAUTL-1, stdin);
        library[count].author[strlen(library[count].author)-1] = '\0';
        printf("Now enter the value: ");
        scanf("%f", &library[count++].value);
        if(getchar() == '\n')
            ;
        printf("Enter the next title: ");
    }
    if(count > 0){
        printf("Here is the list of your books: \n");
        for(index=0; index<count; index++)
            printf("%s by %s: $%.2f.\n", library[index].title,
                library[index].author, library[index].value);
    }
    else
        printf("No books? Too bad.\n");

    return 0;
}

Quote:

Please enter the book title. Please ENTER at the start of line to quit.
The C programming
Now enter the author: K&R
Now enter the value: 68
Enter the next title: ABC
Now enter the author: Edf
Now enter the value: 12
Enter the next title:
Here is the list of your books:
The C programming by K&R: $68.00.
ABC by Edf: $12.00.
Please enter the book title. Please ENTER at the start of line to quit.

No books? Too bad.

请各位大侠指教了，谢谢

[解决办法]

不要使用
while (条件)
更不要使用
while (组合条件)
要使用
while (1) {
 if (条件1) break;
 //... 
 
 if (条件2) continue;
 //...
 if (条件3) return;
 //...
}
因为前两种写法在语言表达意思的层面上有二义性，只有第三种才忠实反映了程序流的实际情况。
典型如：
下面两段的语义都是当文件未结束时读字符
whlie (!feof(f)) {
 a=fgetc(f);
 //...
 b=fgetc(f);//可能此时已经feof了！
 //...
}
而这样写就没有问题：
whlie (1) {
 a=fgetc(f);
 if (feof(f)) break;
 //...
 b=fgetc(f);
 if (feof(f)) break;
 //...
}
类似的例子还可以举很多。

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