《C语言程序设计》第4版 何钦铭、颜晖主编 课后习题答案 第12章 课后习题

P304

练习12-1

文件缓冲区：内存中用于数据存储的数据块，在文件处理过程中，程序需要访问该缓冲区实现数据的存取。

在C程序中，文件类型指针主要的功能是：指向文件的缓冲区，通过移动指针实现对文件的操作。

P306

练习12-2

#include //练习12-2 
#include
main()
{
	int i,offset;
	char pw[80];
	FILE *fp;
	if((fp=fopen("凯撒密码.txt","w"))==NULL){
		printf("文件打开失败！");
		exit(0);
	}
	printf("输入一个正整数offset:");
	scanf("%d",&offset);
	getchar();//接受空格 
	printf("请输入一个字符串：");
	gets(pw); 
	for(i=0;pw[i]!='';i++)//循环取出 
	{
		if(pw[i]>='A'&&pw[i]<='Z'){//经检验，程序没有问题，可能是编译器的问题，字母B和b无法输出。（即输入Z 应输出B，无法正常显示）。 
			if((pw[i]+offset)<'Z'){//未超过最大的字母 
				pw[i]+=offset;
			}else pw[i]=pw[i]-('Z'-offset);//越界，倒着减 
		}else if(pw[i]>='a'&&pw[i]<='z'){
			if((pw[i]+offset)<'z'){
				pw[i]=pw[i]+offset;
			}else pw[i]=pw[i]-('z'-offset);
		}else pw[i]=pw[i];
	}
	fprintf(fp,"%s",pw);
	
	fclose(fp);
}

P311

第一问：判断文件是否结束，EOF是文件结束符。

#include//练习12-3 
#include
int main(void)
{
	FILE *fp1,*fp2;
	int count=0;
	char ch,ch1;
	
	if((fp1=fopen("f12-2.txt","r"))==NULL){
		printf("文件f12-2打开失败！");
		exit(0); 
	}
	if((fp2=fopen("f12-3.txt","w"))==NULL){
		printf("文件f12-3打开失败！");
		exit(0);
	}
	while(!feof(fp1)){
		ch=fgetc(fp1);
		if(ch!=EOF){
			fputc(ch,fp2);
		}
	}
	fclose(fp1);
    fclose(fp2);
    if((fp2=fopen("f12-3.txt","r"))==NULL){
		printf("文件f12-3打开失败！");
		exit(0);
	}
	while(!feof(fp2)){
		ch1=fgetc(fp2);
		if(ch1!=EOF){
			if(ch1!=' ')//包括了回车，有5个 
				count++;
		}
	}
	printf("f12-3中的字符数量为：%d",count);
    
    fclose(fp2);
    
	return 0;
}

P317 

练习12-4到12-6

#include//练习12-4 
#include
int main(void)
{
	FILE *fp;
	char ch;
	int count=1;
	
	if((fp=fopen("letter.txt","r"))==NULL){
		printf("文件打开失败！");
		exit(0);
	}
	while(!feof(fp)){
		ch=fgetc(fp);
		if(ch!=EOF){
			if(ch>='A'&&ch<='Z'){
				ch=ch+32;
			}
			if(ch=='n') count++;
		}
		printf("%c",ch);
	}
	printf("n共%d行",count);
	
	return 0;
}

#include//练习12-5 
#include
int main(void)
{
	FILE *fp;
	char ch,ch1;
	
	if((fp=fopen("f3.txt","w+"))==NULL){
		printf("文件打开失败！");
		exit(0);
	}
	printf("请输入一行字符：");
	while((ch=getchar())!='n'){
		fprintf(fp,"%c",ch);
	}
	rewind(fp);
	while(!feof(fp)){
	    ch=fgetc(fp);  //用fscanf会将最后一个字符重复输出两遍     
		if(ch!=EOF) printf("%c",ch);
	}

	fclose(fp);
	
	return 0;
}

#include//练习12-6 实数取整写入文件 
#include
void splitfloat(double x,int *intpart,double *fracpart)
{
	*intpart=(int)x;//强制转换为整型 
	*fracpart=x-*intpart;//直接减去整数部分可得小数部分 
}
int main(void)
{
	FILE *fp1,*fp2;
	int intpart;//x=345.89，小数部分为0.890015 
	double z,fracpart,a;//x=123.456，小数部分会输出为0.456001
	
	if((fp1=fopen("f1.txt","r"))==NULL){
		printf("文件f1打开失败！"); 
		exit(0);
	}
	if((fp2=fopen("f2.txt","w"))==NULL){
		printf("文件f2打开失败！"); 
		exit(0);
	}
	while(!feof(fp1)){
		fscanf(fp1,"%lf",&z);//读取 
		if(z!=EOF){ 
		    splitfloat(z,&intpart,&fracpart);//拆分整数和小数部分 
//	        printf("整数部分：%dn小数部分：%lfn",intpart,fracpart);//帮助检验 
			if(fracpart>=0.5){//小数部分 四舍五入 
				intpart=intpart+1;
//				printf("整数部分：%dn小数部分：%lfn",intpart,fracpart);//帮助检验     
			}
			fprintf(fp2,"%dn",intpart);
		}
	}
	
	return 0;
}

P321

练习12-7

#include"stdio.h"//练习12-7 
#include"stdlib.h"
#include"process.h"
#include"string.h"
long size;
struct LogData{
	long logid;
	char logdate[11];
	char lognote[15];
	double charge;
	double balance;
};

int inputchoice()
{
	int mychoice;
	printf("nEnter your choice:n");
	printf("1-Add a new cash LOG.n2-List All Cash LOG.n");
	printf("3-Query Last Cash LOG.n4-Update a LOGn0-End program.n");
	scanf("%d",&mychoice);
	return mychoice;
}

long getLogcount(FILE *cfptr)
{
	long begin,end,logcount;
	fseek(cfptr,0L,SEEK_SET);
	begin=ftell(cfptr);
	fseek(cfptr,size,SEEK_END);
	end=ftell(cfptr);
	logcount=(end-begin)/size-1;
	return logcount;
}

void ListAllLog(FILE *cfptr)
{
	struct LogData log;
	fseek(cfptr,0L,SEEK_SET);
	fread(&log,size,1,cfptr);
	printf("logidtlogdata tlognote tchargettbalancen");
	while(!feof(cfptr)){
		printf("%ldt%st%st%.2lftt%.2lfn",log.logid,log.logdate,log.lognote,log.charge,log.balance);
		fread(&log,size,1,cfptr);
	}
}

int QueryLastLog(FILE *cfptr)
{
	struct LogData log;
	long logcount;
	int flag=0;
	logcount=getLogcount(cfptr);
	if(logcount>0)
	{
		fseek(cfptr,size*(logcount-1),SEEK_SET);
		fread(&log,size,1,cfptr);
		flag=1;
		printf("The last log is:n");
		printf("logid:%-6ldnlogdate:%-11snlognote:%-15sn",log.logid,log.logdate,log.lognote);
		printf("charge:%-10.2lfnbalance:%-10.2lfn",log.charge,log.balance);
	}
	else printf("no logs is file!n");
	return flag;
}

void AddNewLog(FILE *cfptr)
{
	struct LogData log,lastlog;
	long logcount;
	printf("Input logdate(format:2006-01-01):");
	scanf("%s",log.logdate);
	printf("Input lognote:");
	scanf("%s",log.lognote);
	printf("Input Charge:Income+and expend-:");
	scanf("%lf",&log.charge);
	logcount=getLogcount(cfptr);
	
	if(logcount>0){
		fseek(cfptr,size*(logcount-1),SEEK_SET);
		fread(&lastlog,size,1,cfptr);
		log.logid=lastlog.logid+1;//记录号按顺序是上次的号+1
		log.balance=log.charge+lastlog.balance ;
	}
	else {
		log.logid=1;
		log.balance=log.charge;
	}
	rewind(cfptr);
	printf("logid=%ldn",log.logid);
	fwrite(&log,sizeof(struct LogData),1,cfptr);
}

void UpdateLog(FILE *cfptr)//修改 ，先查询再修改 
{
	FILE *fp;
	struct LogData log[1000],newlog,*plog=log;
	long id,logcount,i,index=-1;
	char ch;
	printf("请输入一个记录ID：");
	scanf("%ld",&id);
	logcount=getLogcount(cfptr);	//获取记录数 
	rewind(cfptr);
	fread(plog,size,logcount,cfptr);		
	for(i=0;i=0){//没有找到 
		printf("Input logdate(format:2020-01-01):");
		scanf("%s",newlog.logdate); 
		printf("Input lognote:");
		scanf("%s",newlog.lognote); 
		printf("Input Charge:Income+ and expend-:");
		scanf("%lf",&newlog.charge);
		if(strcmp(log[index].lognote,newlog.lognote)!=0)//比较，如果不相同，则修改 
    		strcpy(log[index].lognote,newlog.lognote); 
		if(strcmp(log[index].logdate,newlog.logdate)!=0) 
			strcpy(log[index].logdate,newlog.logdate); 
		if(newlog.charge!=log[index].charge){//如果输入的收支额度改变，重新计算余额 	
  			newlog.balance=log[index].balance-log[index].charge+newlog.charge; 
    		log[index].charge=newlog.charge;	
    		log[index].balance=newlog.balance;
    		for(i=index+1;i