C Primer Plus 第十六章 编程练习 1-7题

第2题

#include<stdio.h>
#define TK(X,Y) 1/((1/X+1/Y)/2)
int main(void)
{
  int i = 10;
  int j = 5;
  printf("结果为%.2lf.",TK((double)i,(double)j));
  return 0;
}

第3题

#include<stdio.h>
#include<math.h>
#define MID 3.1415926/180   //角度转化弧度
struct rectPoint   //直角坐标
{
  double X;
  double Y;
};
struct lenPoint   //极坐标
{
  double angle;
  double Len;
};
struct rectPoint changeCoordinate(const struct lenPoint* LP);
int main(void)
{
  struct rectPoint simpleRect;
  struct lenPoint simpleLen;
  printf("请输入坐标角度:");
  scanf("%lf",&(simpleLen.angle));
  printf("请输入坐标向量长度:");
  scanf("%lf",&(simpleLen.Len));
  simpleRect = changeCoordinate(&simpleLen);
  printf("该向量直角坐标为X:%.2lf Y:%.2lf\n",simpleRect.X,simpleRect.Y);

  return 0;
}
struct rectPoint changeCoordinate(const struct lenPoint* LP)
{
  struct rectPoint RP;
  RP.X = (LP->Len) * cos(LP->angle*MID);
  RP.Y = (LP->Len) * sin(LP->angle*MID);
  return RP;
}

第5题

#include<stdio.h>
#include<time.h>
#include<stdlib.h>
#define LEN 100
#define IX 5  
void showArray(const int* ar , int nu);
void chooseArray(const int* ar , int Len , int nu);
int main(void)
{
  srand((unsigned)time(NULL));
  int testArray[LEN];
  for(int i = 0 ; i < LEN ; ++i)
    testArray[i] = rand()%(LEN);
  showArray(testArray,LEN);
  chooseArray(testArray,LEN,IX);

  return 0;
}
    
void showArray(const int* ar , int nu)
{
  for(int i = 1 ; i <=nu ; ++i)
  {
    printf("%-4d",*(ar+(i-1)));
    if(i%10 == 0)
      printf("\n");
  }
}
void chooseArray(const int* ar , int Len , int nu)
{
  int index[nu];
  for(int i = 0 ; i < nu ; ++i)
    index[i] = rand()%Len;
  for(int i = 0 ; i < nu ; ++i)
  {
    for(int j = i ; j < nu ; ++j)
    {
      int mid;
      if(index[i] > index[j])
      {
        mid = index[i];
        index[i] = index[j];
        index[j] = mid;
      }
    }    
  } 
  for(int i = 0 ; i < nu ; ++i)
    printf("第%d个数为%d\n",index[i]+1,*(ar+index[i]));
}

第6题

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#define Len 50
#define nu 5
struct names
{
  char firstName[Len];
  char lastName[Len];
};
void showArray(const struct names* NM , int len);
int mycomp(const void* pt , const void* pi);
int main(void)
{
  struct names classA[nu] = {
    {"aa","aaa"},
    {"bb","bbb"},
    {"ff","fff"},
    {"dd","ddd"},
    {"ee","eee"},    };
  showArray(classA,nu);
  qsort(classA,nu,sizeof(struct names),mycomp);
  showArray(classA,nu);

  return 0;
}
void showArray(const struct names* NM , int len)
{
  for(int i = 0 ; i < len ; ++i)
    printf("第%d个人名叫%s.%s\n",i+1,(NM+i)->firstName,(NM+i)->lastName);
}

int mycomp(const void* pt , const void* pi)
{
  const struct names* N1 = (const struct names*)pt;
  const struct names* N2 = (const struct names*)pi;
  int res = strcmp(N1->lastName,N2->lastName);
  if(res != 0)
    return res;
  else
    return strcmp(N1->firstName,N2->firstName);
}