求助：为什么输不出+号？

C/C++ code

//问题一：输入2 3 +'\n'输不出+号，但输入2 3 + '\n'时就能输出+号，为嘛？#include <stdio.h>#include <ctype.h>#define NUM 'f'int line = 0;int c = 0;int getop(void){    while ((c = getchar())== ' ' || c == '\t')    {         ;    }    if (!isdigit(c))    {        return c;    }        stdin->_ptr--;    scanf("%d", &line);    return NUM;}void main(){    int number = 0;    int oper = 0;    printf("input:\n");    while (getop() != '\n')    {        printf("c = %c\n", c);    }}//问题二：输入2 3 + 4 +'\n' 输不出最后一个+号，但输入2 3 + 4 + '\n'就能输出最后一个+号，为嘛？#include <stdio.h>#include <ctype.h>#define NUM 'f'void main(){    int number = 0;    int oper = 2;    printf("input:\n");    while (oper != '\0')    {        if (scanf("%d", &number) == 1)        {            printf("number = %d\n", number);            oper = NUM;        }        else if (*stdin->_ptr == '\n' || *stdin->_ptr == ' ')        {            stdin->_ptr--;            if (scanf("%c", &oper) == 1)            {                printf("oper = %c\n", oper);            }                                }        else if (scanf("%c", &oper) == 1)        {            printf("oper = %c\n", oper);        }    }    }

C/C++ code

#include <stdio.h>char s[]="123 ab 4";char *p;int v,n,k;void main() {    p=s;    while (1) {        k=sscanf(p,"%d%n",&v,&n);        printf("k,v,n=%d,%d,%d\n",k,v,n);        if (1==k) {            p+=n;        } else if (0==k) {            printf("skip char[%c]\n",p[0]);            p++;        } else {//EOF==k            break;        }    }    printf("End.\n");}//k,v,n=1,123,3//k,v,n=0,123,3//skip char[ ]//k,v,n=0,123,3//skip char[a]//k,v,n=0,123,3//skip char[b]//k,v,n=1,4,2//k,v,n=-1,4,2//End.
[解决办法]
我在你的上面加了一行，验证了我的想法是对的：
C/C++ code
#include <stdio.h>#include <ctype.h>#define NUM 'f'int line = 0;char c = 0;int getop(void){    while ((c = getchar())== ' ' || c == '\t')    {         ;    }    if (!isdigit(c))    {        return c;    }        stdin->_ptr--;    stdin->_cnt++;/*这里加上以后，你说的那个现象不存在了，哎，冥思苦想了一夜 啊！！看来要好好学习啊！！*/   scanf("%d", &line);    printf("%d\n",line);    return NUM;}int  main(){    int number = 0;    int oper = 0;    printf("input:\n");    while (getop() != '\n')    {        printf("c = %c\n", c);    }}