C和指针课后习题（第四章）

4.1

#include <stdio.h>
#include <math.h>
#include <assert.h>

float fun(float a,float number)
{
float b = (a+(number/a))/2;
return b;
}
int main()
{
float number;
float a=1,b;
printf("please input a number:\n");
scanf("%f",&number);
assert(number>=0);
b = fun(a,number);
printf("a=%f\tb=%f\n",a,b);
printf("%f\n",fabs(a-b));
while(fabs(a-b)>=1e-6)
{
a = b;
b = fun(a,number);
printf("a=%f\tb=%f\n",a,b);
}
return 0;
}

4.2
#include <stdio.h>
#include <assert.h>
int prime(int number)
{
int temp=0;
int i;
for(i=2;i<number;i++)
if(number%i==0)
break;
if(number==i)
{
printf("prime: %d ",number);
return 1;
}
else
return 0;
}
int main()
{
int i,j=0;
printf("the prime number is:\n");
for(i=2;i<=100;i++)
{
//prime(i);
if((j+1)%5==0)
printf("\n");
//j = j+1;
//printf("j=%d\n",j);
if(prime(i)==1)
j = j+1;
}
return 0;

}

4.3
#include <stdio.h>
#include <assert.h>
int main()
{
float a,b,c;
printf("please input three numbers:\n");
scanf("%f%f%f",&a,&b,&c);
assert(a>0&&b>0&&c>0);
assert((a+b)>c&&(b+c)>a&&(a+c)>b);
if(a==b==c)
printf("等边三角形!\n");
else
if(a==b||a==c||c==b)
printf("等腰三角形!\n");
else
printf("普通三角形!\n");
return 0;

}

4.4
#include <stdio.h>
#include <malloc.h>
#include <error.h>
#include <string.h>
#define MAX_LENGTH 100
#define NDEBUG
#include <assert.h>
void copy_n(char dst[],char src[],int n)
{
int i=0;
int length=0;
while(src[i++]!='\0')
length++;
if(length>=n)
for(i=0;i<n;i++)
{
dst[i] = src[i];
dst
='\0';
}
else
{
for(i=0;i<length;i++)
dst[i] = src[i];
for(i=length;i<=n;i++)
dst[i] = '\0';
}

}
int main()
{
char *dst,*src;
int number;
int i;
src = (char *)malloc(sizeof(char)*MAX_LENGTH);
if(src==NULL)
{
perror("Wrong location!\n");
printf("the error is %s\n",strerror(errno));
exit(1);
}
printf("please input a string:\n");
gets(src);
//puts(src);
//fllush(stdin);
setbuf(stdin,NULL);
printf("how many charactor do you want to copy?\n");
scanf("%d",&number);
assert(number>0);
//printf("number=%d\n",number);
dst = (char *)malloc(sizeof(char)*(number+1));
if(dst==NULL)
{
perror("Wrong location!\n");
printf("the error is %s\n",strerror(errno));
exit(1);
}

memset(dst,0,number+1);
//printf("zxc\n");
copy_n(dst,src,number);
//printf("number=%d\n",number);
printf("the string of src is:");
puts(src);
printf("the string of dst is:");
puts(dst);
return 0;
}
4.5

#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <stdlib.h>
//define NDEBUG
#define MAX_LINE 128
#include <assert.h>
int main()
{
char *filename="/home/tony/ZF/1.txt";
FILE *fp=NULL;
if((fp=fopen(filename,"w+"))==NULL)
{
perror("You goofed!");
printf("error=%d.\n",errno);
printf("the error is %s\n",strerror(errno));
return -1;
}
char string[MAX_LINE];
char finish[]="Finished!";
char **cmp;
int i,j,number=0;
puts("please input a string:\n");
while(1)
{
gets(string);
if(strcmp(string,finish)==0)
break;
fprintf(fp,"%s",string);
fprintf(fp,"\n");
number++;
}
fclose(fp);
int *a = (int *)malloc(sizeof(int)*number);
memset(a,0,number);
printf("the number is %d\n",number);
if((fp=fopen(filename,"r"))==NULL)
{
perror("You goofed!");
printf("error=%d.\n",errno);
printf("the error is %s\n",strerror(errno));
return -1;
}
if((cmp=(char **)malloc(sizeof(char*)*(1+number)))==NULL)
{
perror("You goofed!");
printf("error=%d.\n",errno);
printf("the error is %s\n",strerror(errno));
return -2;
}
for(i=0;i<number;i++)
{
if((cmp[i]=(char *)malloc(sizeof(char)*MAX_LINE))==NULL)
{
perror("You goofed!");
printf("error=%d.\n",errno);
printf("the error is %s\n",strerror(errno));
return -3;
}
}
i = 0;
while(1)
{
fgets(string,MAX_LINE,fp);
printf("%s",string);
strcpy(cmp[i++],string);
if(i==number)
break;
}
fclose(fp);
printf("\nthe string is:\n");
for(i=0;i<number;i++)
puts(cmp[i]);
printf("the same string is:\n");
for(i=0;i<number-1;i++)
{
//if(strcmp(cmp[i],"$$$")==0)
// continue;
for(j=i+1;j<number;j++)
{
if(strcmp(cmp[i],cmp[j])==0)
{
//cmp[j]="$$$";
//puts(cmp[i]);
if(-1 == a[i])
a[i]+=0;
else
a[i]+=1;

a[j] = -1;
}

}
}
for(i=0;i<number;i++)
{
//printf("%d\t",a[i]);
if(a[i]>0)
puts(cmp[i]);
}

return 0;

}


4.6
#include <stdio.h>
#include <string.h>
#include <malloc.h>
#include <errno.h>
#include <assert.h>

int substr(char dst[],char src[],int start,int len)
{
int src_length;
int i = 0,j;
src_length = strlen(src);
if(start<0||len<0)
{
dst = "";
printf("the string of dst is:%s\n",dst);
return 0;
}
else if(start+len>=src_length)
{
j = start;
while(src[j]!='\0')
{
dst[i++] = src[j++];
}
dst[i] = '\0';
printf("the string of dst is:%s\n",dst);
return (start+len)-src_length;
}
else
{
for(j=start;j<(start+len);j++)
dst[i++] = src[j];
dst[i] = '\0';
printf("the string of dst is:%s\n",dst);
return len;
}

}
int main()
{
char *dst,*src;
int start,len;
src = (char *)malloc(sizeof(char)*128);
//dst = (char *)malloc(sizeof(char)*len);
printf("the source string is: %s\n",src);
gets(src);
printf("start and len:\n");
scanf("%d%d",&start,&len);
dst = (char *)malloc(sizeof(char)*len);
substr(dst,src,start,len);
return 0;
}

4.7
#include <stdio.h>
#include <malloc.h>
#include <stdlib.h>
#include <errno.h>

void deblank(char string[])
{
int i = 0,j,k;
while(string[i]!='\0')
{
k = 0;
while(string[k++]!='\0')
{
if(' ' == string[k] && ' '==string[k+1])
{
for(j=k;string[j]!='\0';j++)
string[j] = string[j+1];
}
}
i++;
}
}
int main()
{
char *string;
string = (char *)malloc(sizeof(char)*128);
printf("please input a string:\n");
gets(string);
printf("the string is: %s\n",string);
deblank(string);
printf("the string is: %s\n",string);
return 0;
}