C語言程序設計（第2版）課件 藺德軍12 函數(shù)(一)

函數(shù)

本章涉及指針,需要先學數(shù)組、指針部分內容本章主要內容函數(shù)的定義頭文件的產(chǎn)生函數(shù)定義過程簡單參數(shù)傳遞變量的作用范圍函數(shù)的嵌套函數(shù)使用事例#include"stdio.h"doublefun(intn){/*函數(shù)定義*/ inti; doublel=1; if(n<2)return1; elsefor(i=2;i<=n;i++)l*=i;

returnl;}intmain(){intn,m;doublec;printf("輸入nm:\n");scanf("%d%d",&n,&m);c=fun(n)/(fun(m)*fun(n-m));/*調用函數(shù)*/

printf("%lf",c);}問題:計算

c=n!/(m!(n-m)!)n和m都是輸入的整數(shù)函數(shù)的定義函數(shù)定義格式:[返回值類型]函數(shù)名(形式參數(shù)表){函數(shù)體}說明:類型說明符省略時,相當于整形函數(shù)中聲明的參數(shù)稱為形式參數(shù)，調用時代入的值稱為實際參數(shù)形式參數(shù)表可以為空,但是兩側的()不能省略函數(shù)用return語句返回值,返回值類型必須與函數(shù)頭聲明的返回類型一致沒有返回值時,類型應聲明成void,這種情況下,可以沒有return語句或用空return函數(shù)必須先聲明后使用，如果函數(shù)說明出現(xiàn)在調用之后時，要先用函數(shù)頭說明函數(shù)舉例:floatarea(floatradius){floata;a=3.14*radius*radius;returna;}函數(shù)聲明在main函數(shù)后時#include"stdio.h"doublefun(intn);/*函數(shù)的原型聲明,還可以寫作double(int任意變量名)或doublefun(int)*/intmain(){intn,m;doublec;printf("輸入nm:\n");scanf("%d%d",&n,&m);c=fun(n)/(fun(m)*fun(n-m));/*調用函數(shù)*/ printf("%lf",c);}doublefun(intn){/*函數(shù)定義*/ inti; doublel=1; if(n<2)return1; elsefor(i=2;i<=n;i++)l*=i; returnl;}頭文件的產(chǎn)生

函數(shù)定義過程1.函數(shù)返回數(shù)值類型是什么2.函數(shù)名叫什么3.函數(shù)要接受幾個參數(shù)，分別是什么類型4.函數(shù)實現(xiàn)，使用參數(shù)，計算結果5.返回結果6.一般函數(shù)只是來料加工，不包含輸入輸出函數(shù)的定義與執(zhí)行引用(C++選學)//引用就是別名,給一個變量多個名字#include<stdio.h>intmain(){ inta=20,&y=a; y=30; printf("%d\n",a);}參數(shù)傳遞方式值傳遞地址傳遞引用傳遞參數(shù)傳遞-數(shù)值傳遞#include<stdio.h>voidf(intb){ b++; printf("b=%d\n",b);}intmain(){inta=1;f(a); printf("a=%d\n",a);;}參數(shù)傳遞-地址傳遞#include<stdio.h>voidf(int*b){ (*b)++; printf("*b=%d\n",*b);}intmain(){inta=1;f(&a); printf("a=%d\n",a);}參數(shù)傳遞-引用傳遞(選學)#include<stdio.h>voidf(int&b){ b++; printf("b=%d\n",b);}intmain(){inta=1;f(a); printf("a=%d\n",a);}參數(shù)傳遞舉例#include"stdio.h"voidfun(int*b){intt=5;printf("1thb=%d\n",*b);

*b=t;/*給*b(變量a)賦值*/printf("2thb=%d\n",*b);}intmain(){m1:inta=2;m2:fun(&a);m3:printf("3tha=%d\n",a);}#include"stdio.h"voidfun(int*b){intt=5;printf("1thb=%d\n",*b);

b=&t;/*給變量b賦值t的地址*/printf("2thb=%d\n",*b);}intmain(){m1:inta=2;m2:fun(&a);m3:printf("3tha=%d\n",a);}參數(shù)傳遞舉例#include<stdio.h>voidf(inta,int*b){ intt; t=a;a=*b;*b=t;}intmain(){intx=2,y=3;f(x,&y); printf("%d,%d\n",x,y);}變量作用范圍全局級變量：全局有效函數(shù)級變量：本函數(shù)內有效復合語句級變量：本復合語句內有效當出現(xiàn)不同級別變量重名時，遵從局部優(yōu)先原則，最內層有效變量作用范圍示例（一）#include<stdio.h>inta;voidf(intb){ intc; a=1; b=2; d=3;}intmain(){ intd; { inte; a=1; b=2; c=3; d=4; e=5; } a=1; b=2; c=3; d=4; e=5;}變量作用范圍示例（二）#include<stdio.h>inta=10;voidf1(){a++;printf("f1:%d\n",a);}voidf2(){inta=-5;a++;printf("f2:%d\n",a);}intmain(){ inta=1;//刪除后再運行一次

a++; printf("1:%d\n",a); {inta=-3;a++;printf(“2:%d\n",a);} printf(“3:%d\n",a); {a++;printf(“4:%d\n",a);}printf(“5:%d\n",a); f1(); printf(“6:%d\n",a); f2(); printf(“7:%d\n",a);}嵌套#include<stdio.h>voidf1(){ putchar('1');putchar('2');}voidf2(){putchar('3');f1();putchar('4');}intmain(){ putchar('5');f2();putchar('6');}函數(shù)舉例-1//問題：用牛頓迭代法求方程f(x)=2*x*x*x-4*x*x+3*x-6根//x=x0-f/f'#include<stdio.h>#include<math.h>doublef(doublex){ return2*x*x*x-4*x*x+3*x-6;}doublefb(doublex){ return6*x*x-8*x+3;}intmain(){ doublex0,x=0; x0=3.0; x=x0-f(x0)/fb(x0); while(fabs(x-x0)>1e-5){ x0=x;x=x0-f(x0)/fb(x0); } printf("%lf\n",x); }函數(shù)舉例-21.分別用矩形法和梯形法求#include<stdio.h>#include<math.h>doublef(doublex