3.函数简介

1.函数有主函数(main)和一般函数之分,主函数可以调用一般函数,反之则不可以.
2.一般函数之间可以相互调用,如果直接或间接调用自身则为直接或间接递归.
3.函数返回值有三种:
1)void类型,只能作为函数语句使用
2)简单类型(如:int , int * 等等)或记录类型(如:student,person等等)
3)简单类型或记录类型的引用( 如: int&, student&等)
举例如下:
#include "iostream.h"
#include "string.h"
#include "stdlib.h"

const int PN = 5;
struct pupil
{
        char pnum[8];  //学号
        int grade;     //分数
};

//超前说明三个重载函数的原型
int    find(pupil b[],int n,char* k);
pupil* find(int n,pupil b[],char* k);
pupil& find(char* k,pupil b[],int n);

void main()
{
        pupil a[PN] = {{"010203",78},{"010204",92},{"020101",85},{"020301",63},{"040502",87}};
        int i;
        for(i = 0;i < PN;i++)
        {
                cout<<a[i].pnum<<" "<<a[i].grade<<endl;
        }
        cout<<endl;
        pupil x = {"020101",98};
        cout<<"请输入您的选择(1,2,3)?";
        cin>>i;
        switch(i)
        {
                case 1:
                        i = find(a, PN, x.pnum);
                        if (i < PN)
                        {
                                a[i] = x;
                        }
                        else
                        {
                                cout<<x.pnum<<"not found!"<<endl;
                        }
                        break;
                case 2:
                        pupil* p;
                        p = find(PN, a, x.pnum);
                        if (p != NULL)
                        {
                                *p = x;
                        }
                        else
                        {
                                cout<<x.pnum<<"not found!"<<endl;
                        }
                        break;
                case 3:
                        find(x.pnum,a,PN) = x ;
        }
        for(i = 0;i < PN;i++)
        {
                cout<<a[i].pnum<<" "<<a[i].grade<<endl;
        }
}
int find(pupil b[],int n,char* k) //返回元素下标
{
        for(int i = 0;i < n;i++)
        {
                if (strcmp(b[i].pnum,k) == 0)
                {
                        return i;
                }
        }
        return i;
}

pupil* find(int n,pupil b[],char* k)
{
        for(int i = 0;i < n;i++)
        {
                if (strcmp(b[i].pnum,k) == 0)
                {
                        return &b[i];
                }
        }
        return NULL;
}

pupil& find(char* k,pupil b[],int n)
{
        for(int i = 0;i < n;i++)
        {
                if (strcmp(b[i].pnum,k) == 0)
                {
                        return b[i];
                }
        }
        cerr<<k<<"not found!"<<endl;
        exit(1);
}