测试getchar()== EOF无法正常工作 [英] Testing getchar() == EOF doesn't work as expected

问题描述

我有一个任务写一个C程序，该程序允许用户输入最多20个整数(它将停止接受基于前哨值或达到20个整数的数字).然后，该程序应以相反的顺序显示数字."

I have an assignment to "Write a C program that allows a user to enter up to 20 integers (it will stop accepting numbers based on a sentinel value or based on the 20-integer limit being reached). The program should then display the numbers in the reverse order of entry."

我决定将前哨值设为"EOF"(或CTRL + D/CRTL + Z).我的代码有一些非常不稳定的行为:

I decided to make my sentinel value "EOF" (or CTRL+D / CRTL+Z). My code has some really erratic behavior:

1. 您必须按两次EOF键(这还会创建一个空白条目，该条目将计入数组.
2. 第一个条目的第一位被截断.

其他一切似乎都可以，但是，这显然不是期望的结果.下面是我的代码.您能解释出什么问题吗?

Everything else seems to work OK but, this is clearly not the desired results. Below is my code. Can you explain what's wrong?

main() {
int i,iMax;
double dblMean;
int x[MAX];

printf("Please Enter Up to 20 Integers\n");

for (i=0; i<MAX; i++)
{
    printf("%d.> ",i+1);
    if (getchar() == EOF)           /* Check for CTRL+D OR CTRL+Z */
    break;                          /* Exit loop if EOF entered :: Must be pressed twice and eats first character of first entry */
    scanf("%d",&x[i]);
    iMax=i;
}

printf("\nYou entered  %d numbers\n",iMax+1);               /* Should be i+1 but EOF had to be entered twice */
printf("\nIndex       Item        Reverse Item\n");
for (i=0; i<=iMax; i++)
    printf("%3d%4c%8d%9c%11d\n",i,'  ',x[i],'  ',x[iMax-i]);
return 0;

}

这是我的最终代码，谢谢大家的帮助:

EDITED: Here is my final code, Thank you all for your help:

#include <stdio.h>
#include <stdlib.h>
#define MAX 20
int main()
{
    int i,iMax;
    int x[MAX];

    printf("Please Enter Up to 20 Integers\n");

    for (i=0; i<MAX; i++)
    {
        printf("%d.> ",i+1);
        if (scanf("%d",&x[i]) != 1)                         /* Checks for CTRL+D OR CTRL+Z */
        break;                                              /* EOF returns -1 and loop will be exited */
        iMax=i;                                             /* iMax must be set for second loop to exit properly */
                                                            /* Can sizeof x be used instead for second loop? */
    }

    printf("\nYou entered  %d numbers\n",iMax+1);           /* Displays number of items entered... Will be <= MAX*/
    printf("\nIndex       Item        Reverse Item\n");
    for (i=0; i<=iMax; i++)                                 /* Why wont 'for (i=0; i<=sizeof x; i++)' work? */
        printf("%3d%4c%8d%9c%11d\n",i,'  ',x[i],'  ',x[iMax-i]);
    return 0;
}

推荐答案

getchar()调用读取(并有效丢弃)第一位数字，因为它不是EOF.

The getchar() call reads (and effectively discards) the first digit because it is not EOF.

您无需测试scanf()是否有效；你应该.

You don't test that scanf() worked; you should.

for (i = 0; i < MAX; i++)
{
    if (scanf("%d", &x[i]) != 1)
        break;
}

这时，数组中有i个整数.您实际上并不需要在循环中设置iMax.您只需在循环退出时进行设置即可.

At this point, there are i integers in the array; you don't really need to set iMax in the loop. You could simply set it when the loop exits.

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