C语言及程序设计初步例程-8 数值数据类型及表示

贺老师教学链接  C语言及程序设计初步 本课讲解

例：程序中的数据类型、常量、变量

#include <stdio.h>
int main( )
{
    float f,m;
    printf("length in feet: ");
    scanf("%f", &f);
    m = f / 3.28;
    printf("equal to %f meters.\n", m);
    return 0;
}

列出当前系统中各种类型数据占用的字节数

#include <stdio.h>
int main( )
{
    printf("Size of int is: %d\n",sizeof(int));
    printf("Size of short int is: %d\n",sizeof(short));
    printf("Size of long int is: %d\n",sizeof(long));
    printf("Size of unsigned int is: %d\n",sizeof(unsigned int));
    printf("Size of float is: %d\n",sizeof(float));
    printf("Size of double is: %d\n",sizeof(double));
    printf("Size of long double is: %d\n",sizeof(long double));
    printf("Size of char is: %d\n",sizeof(char));
    return 0;
}

程序中慎重直接使用常量——用符号常量替代

#include <stdio.h>
#define PI 3.1415926  //定义符号常量
int main ( )
{
  float r,l,s,sq,vq;
  printf("please enter r,h:");
  scanf("%f %f"), &r, &h);
  l=2* PI *r;
  s=r*r* PI;
  sq=4* PI *r*r;
  ……
} 

对比

/*不用符号常量的程序，注意若的错误*/
#include <stdio.h>
int main ( )
{
  float r,l,s,sq,vq;
  printf("please enter r,h:");
  scanf("%f %f"), &r, &h);
  l=2* 3.1415926 *r;
  s=r*r* 3.1415926;
  sq=4* 3.1445926 *r*r;
  ……
} 

再品符号常量

//程序的问题：可读性差、难维护
#include <stdio.h>
int main ( )
{
    int n, age, total;
    scanf("%d %d", &age, &n);
    if(age<30)
    {
        total=n*30;
        printf("total=%d\n",total);
    }
    else
    {
        printf("done!\n");
    }
    return 0;
}

改进的代码：

#include <stdio.h>
#define PRICE 30  //代表固定的单价
#define AGE 30    //代表年龄
int main ( )
{
    int n, age, total;
    scanf("%d %d", &age, &n);
    if(age<AGE)  //30岁以下的才可以买
    {
        total=n*PRICE;
        printf("total=%d\n",total);
    }
    else
    {
        printf("done!\n");
    }
    return 0;
}