c - C 语言代码上的库菜单程序不起作用

Question

在我的类里面，我被分配制作一个图书馆菜单程序，其中包括

a structure with bookname/author/price/issue date; then a menu with different options like addbook,display, search by author etc

我相信我已经掌握了如何做的基本概念，并且我在代码块中起草了它的草稿。但问题是代码可以正常工作，但我无法仅获得 book name 的输入/输出(我想是在休息)，而且我找不到原因。我是编程的初学者，刚开始编程 2 个月左右，所以如果有人能指出我的代码中的错误，我将非常感激。

提前致谢，这是我的

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

int bookcount=0;
struct library{                                  
char name[100];
char author[100];
float price;
char date[20];
}str[100];

int main(){
    int i;
    menu();
    return 0;
}

int menu(){
    int choice,i;
    for(i=0;;i++){
        printf("\nWelcome to library menu.Please enter a choice from below-");
        printf("\n\nPress 1 to add book information\nPress 2 to Display book information\nPress 3 to search books by author name");
        printf("\nPress 4 to list the count of books\nPress 5 to find all the books for given price\nPress 0 for exit\nChoice=");
        scanf("%d",&choice);
    if(choice==0)
        break;
    else{
        switch(choice){
            case 1:
                addbook();
                break;
            case 2:
                display();
                break;
            case 3:
                searchbyauthor();
                break;
            case 4:
                listcount();
                break;
            case 5:
                findbyprice();
                break;
            default:
                printf("invalid input!\n");
        }
    }
}
return 0;
}


int addbook(){
    int n,i;
    printf("\nEnter number of books to add=");
    scanf("%d",&n);
    for(i=0;i<n;i++){
        printf("\nEnter book title=");
        gets(str[bookcount].name);
        printf("\nEnter book author=");
        gets(str[bookcount].author);
        printf("\nEnter book date=");
        gets(str[bookcount].date);
        printf("\nEnter book price=");
        scanf("%f",&str[bookcount].price);
        bookcount++;
}
return 0;
}

int display(){
    int i;
    for(i=0;i<bookcount;i++){
        printf("\nBook no %d name=",i+1);
        puts(str[i].name);
        printf("\nBook no %d author=",i+1);
        puts(str[i].author);
        printf("\nBook no %d issue date=",i+1);
        puts(str[i].date);
        printf("\nBook no %d price=%f",i+1,str[i].price);
    }
return 0;
}

int searchbyauthor(){
    char inp[100];
    int i;
    printf("\nEnter Author name to search=");
    gets(inp);

    for(i=0;i<bookcount;i++){
        if(strcmp(str[i].author,inp)==0)
            printf("\nBook name=%s",str[i].name);
    }

    return 0;
}

int listcount(){
    printf("\nnumber of books are =%d\n",bookcount);
    return 0;
}

int findbyprice(){
    float inp;
    int i;
    printf("\nEnter price to search=");
    scanf("%f",&inp);

    for(i=0;i<bookcount;i++){
        if(str[i].price==inp)
            printf("\nBook name=%s",str[i].name);
    }

    return 0;
}

Answer 1

由于您没有发布任何输入，我需要自己找出答案，下次只包括采样输入和输出:

1
1
name

让我们看看此时您的程序使用 stdin 做了什么

scanf("%d",&choice); // in menu() in loop, choice := 1, ie add book
scanf("%d",&n); // in addbook(), n := 1, ie. 1 book
gets(str[bookcount].name); // in addbook in loop, this will be and should be ""

scanf() “消耗并丢弃所有前导空白字符”和换行符 is whitespace特点。所以这就是发生的事情:

scanf("%d",&choice); // reads '1' from the input, and stops BEFORE newline
scanf("%d",&n); // discards newline and reads 1 from the input and stops before newline
gets(str[bookcount].name); // because newline is still in buffer and gets 
                           // stops at first newline, this will read empty string
// the next gets will read the `name` from stdin, as it wasn't read already

修复相当简单。只扫描 scanf("%d\n",...); 行而不是单个变量。