循环输入问题，为什么会多输一个

[lvdongfengphp]

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

struct sequence
{
	int MAXCOUNT;			//最大个数
	int top;				//栈顶元素位置
	int *elem;					//
};

typedef struct sequence Seq;

//创建一个空栈,大小为max
Seq *createStack(int max){

	Seq *seq;
	seq = (Seq*)malloc(sizeof(Seq));
	seq->MAXCOUNT = max;
	seq->elem = (int*)malloc(max * sizeof(int));
	seq->top=-1;
	return seq;
}

//判断是否为空栈
int isEmpty(Seq *seq){
	if(seq->top==-1)
		return 0;
	else
		return 1;
}

//进栈
void push(Seq *seq, int m){
	if(seq->top== seq->MAXCOUNT-1){
		printf("overflow\n");
	}else{
		seq->top = seq->top + 1;
		seq->elem[seq->top] = m;
	}
}

//出栈
void pop(Seq *seq){
	if(seq->top==-1){
		printf("underflow\n");
	}else{
		seq->top = seq->top - 1;
	}
}

//取栈顶元素
int gainTopEle(Seq *seq){
	if(seq->top==-1){
		printf("It is empty\n");
		return NULL;
	}
	return (seq->elem[seq->top]);
}
void main(){
	int max;
	printf("请输入栈的大小：");
	scanf("%d",&max);
	Seq *seq = createStack(max);
	printf("请输入栈的元素(-1 结束)：\n");
	/*
	for(int i=0; i<max; i++){
		int num;
		scanf("%d ",&num);
		push(seq, num);
	}
	*/
	int num;

	do{
		scanf("%d ",&num);
		if(num!=-1)
			push(seq, num);
	}while(num!=-1);
	
	while(isEmpty(seq)!=0){
		printf("%d  ", gainTopEle(seq));
		pop(seq);
	}
	printf("\n end \n");
}

当输入-1的时候，为什么后面还要输多一个数才能结束循环呢？

[赵4老师]

将scanf中%d后面的空格去掉再试试。

[zuxi]

scanf("%d ",&num); ---> scanf("%d",&num);

[苏叔叔]

scanf("%d ", &num); //%d后的空格，会匹配最后的回车，导致scanf无法终止 直接使用scanf("%d", &num); 输入数字之间的空格会被scanf跳过，

[苏叔叔]

引用 3 楼 zhangxiangDavaid 的回复:

scanf("%d ", &num); //%d后的空格，会匹配最后的回车，导致scanf无法终止 直接使用scanf("%d", &num); 输入数字之间的空格会被scanf跳过，

两个数字之间的换行同样会被跳过

[赵4老师]

Format Specification Fields: scanf and wscanf Functions A format specification has the following form: %

• [width] [{h | l | I64 | L}]type The format argument specifies the interpretation of the input and can contain one or more of the following: White-space characters: blank (' '); tab ('\t'); or newline ('\n'). A white-space character causes scanf to read, but not store, all consecutive white-space characters in the input up to the next non–white-space character. One white-space character in the format matches any number (including 0) and combination of white-space characters in the input. Non–white-space characters, except for the percent sign (%). A non–white-space character causes scanf to read, but not store, a matching non–white-space character. If the next character in stdin does not match, scanf terminates. Format specifications, introduced by the percent sign (%). A format specification causes scanf to read and convert characters in the input into values of a specified type. The value is assigned to an argument in the argument list. The format is read from left to right. Characters outside format specifications are expected to match the sequence of characters in stdin; the matching characters in stdin are scanned but not stored. If a character in stdin conflicts with the format specification, scanf terminates, and the character is left in stdin as if it had not been read. When the first format specification is encountered, the value of the first input field is converted according to this specification and stored in the location that is specified by the first argument. The second format specification causes the second input field to be converted and stored in the second argument, and so on through the end of the format string. An input field is defined as all characters up to the first white-space character (space, tab, or newline), or up to the first character that cannot be converted according to the format specification, or until the field width (if specified) is reached. If there are too many arguments for the given specifications, the extra arguments are evaluated but ignored. The results are unpredictable if there are not enough arguments for the format specification. Each field of the format specification is a single character or a number signifying a particular format option. The type character, which appears after the last optional format field, determines whether the input field is interpreted as a character, a string, or a number. The simplest format specification contains only the percent sign and a type character (for example, %s). If a percent sign (%) is followed by a character that has no meaning as a format-control character, that character and the following characters (up to the next percent sign) are treated as an ordinary sequence of characters, that is, a sequence of characters that must match the input. For example, to specify that a percent-sign character is to be input, use %%. An asterisk (*) following the percent sign suppresses assignment of the next input field, which is interpreted as a field of the specified type. The field is scanned but not stored.