作用域
- 作用域描述程序中可以访问标识符 的区域.
- 一个C变量的作用域可以是块作用域、函数作用域、函数原型作用域或文件作用域。
- 块是用一对花括号括起来的代码区域
#include <stdio.h>
int main(void)
{
int x;
x = 1;
printf("%d\n", x);
{
int x = 5; // 新的x
printf("%d\n" , x); // x作用域结束
}
printf("%d\n", x); // 原来的x
return 0;
}
链接
C变量用3种属性：外部链接、内部链接或无链接。具有块作用域、函数作用域或函数原型作用域的变量都是无链接变量。
简单来说就是有链接的变量都是全局变量。不过之间也有点不同
存储期
C对象有4中存储期: 静态存储期、线程存储期、自动存储期、动态分配存储期。
- 静态存储期：一直存在
- 线程存储期：从被声明时到线程结束一直存在。
- 自动存储期：当程序进入这些块时分配内存。推出时释放内存
-
动态分配：用特殊的关键字来创建和释放内存
image.png
块作用域的静态变量
#include <stdio.h>
void trystat(void);
int main(void)
{
int count;
for ( count = 1; count <= 3; count++)
{
printf("Here comes iteration %d:\n", count);
trystat();
}
return 0;
}
void trystat(void)
{
int fade = 1; //执行3次都是1
static int stay = 1; //会记录住原来的
printf("fade = %d and stay = %d\n", fade++, stay++);
}
image.png
内部链接的静态变量
该存储类别的变量具有静态存储期、文件作用域和内部链接。定义在所用函数外部(和上面那个不一样)
static int svil = 1; //静态变量，内部链接
int main(void)
{
extern int svil; //使用定义在别处的
｝
注：作用域只有本文件有效
外部链接的静态变量
int Errupt;
int main(void)
1.不使用全局变量， 从写12.4
#include <stdio.h>
int critic(void);
int main(void)
{
int units;
printf("How many pounds to a firkin of butter?\n");
scanf("%d", &units);
while (units != 56)
{
units = critic();
}
printf("You must have looked it up!\n");
return 0;
}
int critic(void)
{
int i;
printf("No luck, my friend. Try again.\n");
scanf("%d", &i);
return i;
}
2
//pe12-2b.c
#include <stdio.h>
#include "pe12-2a.h"
int main(void)
{
int mode;
printf("Enter 0 for metric mode, 1 for US mode: ");
scanf("%d", &mode);
while (mode >= 0)
{
set_mode(mode);
get_info();
show_info();
printf("Enter 0 for metric mode, 1 for US mode");
printf(" (-1 to quit): ");
scanf("%d", &mode);
}
puts("Done");
return 0;
}
//pe12-2a.c
#include <stdio.h>
#include "pe12-2a.h"
static int mode = 0;
static double distance;
static double energy;
void set_mode(int n)
{
if (n == 0 || n == 1)
mode = n;
else
printf("Invalid mode specified.Mode %s used.\n", (mode ? "1(US)" : "0(metric)"));
}
void get_info(void)
{
if (mode == 0)
{
printf("Enter distance traveled in kilometers: ");
scanf("%lf", &distance);
printf("Enter fuel consumed in liters: ");
scanf("%lf", &energy);
}
else
{
printf("Enter distance traveled in miles: ");
scanf("%lf", &distance);
printf("Enter fuel consumed in gallons: ");
scanf("%lf", &energy);
}
}
void show_info(void)
{
double consuption;
if (mode == 0)
{
consuption = energy / distance * 100;
printf("Fuel consumption is %.2lf liters per 100 km\n", consuption);
}
else
{
consuption = distance / energy;
printf("Fuel consumption is %.1lf miles per gallon\n", consuption);
}
}
//pe12-2a.h
void set_mode(int);
void get_info(void);
void show_info(void);
3.重写上面
//pe12-2b.c
#include <stdio.h>
#include "pe12-2a.h"
int main(void)
{
int mode;
int num = 0;
double distance, energy;
printf("Enter 0 for metric mode, 1 for US mode: ");
scanf("%d", &mode);
while (mode >= 0)
{
num = set_mode(num, mode);
get_info(num, &distance, &energy);
show_info(num, distance, energy);
printf("Enter 0 for metric mode, 1 for US mode");
printf(" (-1 to quit): ");
scanf("%d", &mode);
}
puts("Done");
return 0;
}
//pe12-2a.c
#include <stdio.h>
#include "pe12-2a.h"
int set_mode(int n,int m)
{
if (m == 0 || m == 1)
n = m;
else
printf("Invalid mode specified.Mode %s used.\n", (n ? "1(US)" : "0(metric)"));
return n;
}
void get_info(int n, double *distance, double *energy)
{
if (n == 0)
{
printf("Enter distance traveled in kilometers: ");
scanf("%lf", distance);
printf("Enter fuel consumed in liters: ");
scanf("%lf", energy);
}
else
{
printf("Enter distance traveled in miles: ");
scanf("%lf", distance);
printf("Enter fuel consumed in gallons: ");
scanf("%lf", energy);
}
}
void show_info(int mode , double distance, double energy)
{
double consuption;
if (mode == 0)
{
consuption = energy / distance * 100;
printf("Fuel consumption is %.2lf liters per 100 km\n", consuption);
}
else
{
consuption = distance / energy;
printf("Fuel consumption is %.1lf miles per gallon\n", consuption);
}
}
//pe12-2a.h
int set_mode(int, int);
void get_info(int, double *, double *);
void show_info(int, double, double);
4
#include <stdio.h>
int ret_num(void);
int main(void)
{
int i;
ret_num();
i = ret_num();
printf("%d\n", i);
}
int ret_num(void)
{
static int count = 0;
return ++count;
}
5
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define SIZE 100
void stsrt(int *st[], int num);
int main(void)
{
int number[SIZE];
int i;
int *p[SIZE];
srand((unsigned int) time(0));
for ( i = 0; i < SIZE; i++)
{
number[i] = rand() % 10 + 1;
p[i] = &number[i];
}
stsrt(p, SIZE);
puts("排序后:");
for ( i = 0; i < SIZE; i++)
{
printf("%d ", *p[i]);
}
printf("\n");
puts("排序前:");
for ( i = 0; i < SIZE; i++)
{
printf("%d ", number[i]);
}
return 0;
}
void stsrt(int *st[], int num)
{
int *temp;
int top, seek;
int i = 0;
for ( top = 0; top < num - 1; top++)
{
for ( seek = top + 1; seek < num; seek++)
{
if ( *st[top] < *st[seek])
{
temp = st[top];
st[top] = st[seek];
st[seek] = temp;
}
}
}
}
6出自:https://blog.csdn.net/o707191418/article/details/81904734
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
int main(void)
{
int random_[10] = {0};
int i, num;
srand((unsigned int) time(0));
for(i = 0; i < 100; i++)
{
num = rand() % 10 +1;
random_[num - 1]++;
}
for ( i = 0; i < 10; i++)
{
printf("%d : %d\n", i + 1, random_[i]);
}
}
7
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
int roll_n_dice(int , int );
int main(void)
{
int size, dice, many, status;
int i, roll;
srand((unsigned int) time(0));
puts("Enter the number of sets; enter q to stop.");
while (scanf("%d", &many) == 1 && many > 0)
{
puts("How many sides and how many dice?");
if ((status = scanf("%d %d", &size, &dice)) != 2)
{
if (status == EOF)
break;
else
{
puts("You should have entered an integer.");
puts("Let's begin again.");
while (getchar() != '\n')
continue;
puts("Enter the number of sets; enter q to stop.");
continue;
}
}
printf("Here are %d sets of %d %d-sided throws.\n", many, dice, size);
for ( i = 0; i < many; i++)
{
roll = roll_n_dice(dice, size);
printf("%d ", roll);
}
puts("\nEnter the number of sets; enter q to stop.");
}
}
int roll_n_dice(int dice, int size)
{
int total = 0;
int i;
if (size < 2)
{
printf("Need at least 2 sides.\n");
return -2;
}
if (dice < 1)
{
puts("Need at lease 1 die.\n");
return -1;
}
for ( i = 0; i < dice; i++)
{
total += rand() % size + 1;
}
return total;
}
8
#include <stdio.h>
#include <stdlib.h>
int * make_array(int elem, int val);
void show_array(const int ar[], int n);
int main(void)
{
int * pa;
int size;
int value;
printf("Enter the number of elements:");
while (scanf("%d", &size) == 1 && size > 0)
{
printf("Enter the initialization value: ");
scanf("%d", &value);
pa = make_array(size, value);
if (pa)
{
show_array(pa, size);
free(pa);
}
printf("\nEnter the number of elements (<1 to quit): ");
}
printf("Done.\n");
return 0;
}
int * make_array(int elem, int val)
{
int *p;
int i;
p = (int *) malloc(elem * sizeof(int));
for ( i = 0; i < elem; i++)
{
p[i] = val;
}
return p;
}
void show_array(const int ar[], int n)
{
int i;
for ( i = 0; i < n; i++)
{
printf("%d ", ar[i]);
if ((i + 1) % 8 == 0)
printf("\n");
}
}
9https://blog.csdn.net/o707191418/article/details/81904734
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define SIZE 64
int main(void)
{
char **p; //存储字符串
char *temp; //用于零时存储
int words; //单词数量
int len; //计算长度，方便后面拷贝
int i;
printf("How many words do you wish to enter? ");
scanf("%d", &words);
printf("Enter %d words now:\n", words);
p = (char **) malloc(words * sizeof(char *)); //数组里的每一个元素是一个指针，指向char类型(数组里存储的是指向char类型的指针)
temp = (char *) malloc(SIZE * sizeof(char)); //分配一段内存，用于存储字符串
for ( i = 0; i < words; i++)
{
scanf("%s", temp); //输入字符串，scanf将空格回车视为一个单词的结束
len = strlen(temp); //计算单词占多少空间
p[i] = (char *) malloc((len + 1) * sizeof(char)); //p里面每个元素都是一个指针，分配内存让他指向该内存，+1是为了存储\0
strcpy(p[i], temp); //拷贝
}
free(temp); //释放temp的空间
for ( i = 0; i < words; i++)
{
puts(p[i]);
}
free(p); //释放p空间
return 0;
}
