C语言基础有关问题，纠结的IO函数

C语言基础问题，纠结的IO函数
这个函数开始用scanf语句，如注释所示，一直出错，红色部分语句直接跳过了。后来想到用getchar试试，可以，但不知其解，求解答啊。以为是缓冲区问题，各种刷新缓冲区，但是没有解决…………
[code=C/C++][/code]
void Modify(Link l)
{
int selection;
int yesno;
char searchinput[20];
Node *p;
if(!l->next)
  {
system("cls");
printf("\n No Student Record.\n");
printf("Press Any Key To Return...");
_getch();
return;
}
system("cls");
Disp(l);
printf("\n\n\t1 . Search by Number \n\t2 . Search by Name :\n");
printf("Please Enter a Choice : \n\t");
  scanf("%d",&selection);
if(selection==1)
{
StringInput(searchinput,20,"Input Number,Please.");
p=Locate(l,searchinput,"num");
 if(p)
{
PrintFingure();
PrintData(p);
printf(END);
printf("Sure to Modify? (Y/N) ");
  fflush(stdin);
//scanf("%d",&yesno); //为什么不能工作呢？
  yesno=getchar();
//cin>>yesno;
fflush(stdin);
if((yesno=='n')||(yesno=='N'))
{
printf("Press Any Key to Return...\n");
fflush(stdin);
_getch(); 
return;
}
else if(yesno=='Y'||yesno=='y')
{
save_flag=1;
StringInput(p->data.name,15,"Name");
p->data.cgrade=NumberInput("C language Score[0-100] :");
p->data.egrade=NumberInput("English Language Score[0-100] :");
p->data.mgrade=NumberInput("Math Language Score[0-100] :");
p->data.total=p->data.cgrade+p->data.egrade+p->data.mgrade;
p->data.ave=(float)p->data.total/3;
p->data.mingci=0;
printf("\n Modify Successfully.\n");
PrintData(p);
printf("Press Any Key to Return...");
_getch();
}
else
{
printf("Unknown Choice...");
printf("Press Any Key to Return...");
}

}
else
{
printf("No Data related Found.");
printf("Press Any Key to Return...");
}
}

[解决办法]
楼主，你是想用一个int变量输入字符n或N，看下面这程序，你输入N或n时，输出的并不是他们的ASCII码值，所以if((yesno=='n')||(yesno=='N'))这个条件不成立，没执行

C/C++ code

#include<iostream>#include<cstdio>using namespace std;int main(){    int num;    scanf("%d", &num);    printf("%d\n", num);    return 0;}
[解决办法]
仅供参考
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.