第36课 - 变量的作用域与生命期（上）

#include <stdio.h>

int var = 100;  // 全局变量

void f(int var) // var <==> 局部变量
{
    var++;

    printf("var = %d\n", var);
}

int main()
{
    int var = 10;  // 局部变量

    f(var);  // f(10);

    printf("var = %d\n", var);  // var = 10;

    return 0;
}
// var = 11
// var = 10

#include <stdio.h>

int var = 100;  // 全局变量

int main()
{
    int var = 10;  // 局部变量

    {
        int var = 1;  // 局部变量

        printf("var = %d\n", var);
    }

    printf("var = %d\n", var);  // var = 10;

    return 0;
}
var = 1
var = 10

#include <stdio.h>

int main()
{
    int i = 0;  // 局部变量

    while( i < 5 )
    {
        int j = 10;  // 局部变量

        j++;

        printf("j = %d\n", j);

        i++;
    }

    printf("i = %d\n", i);  // var = 10;

    return 0;
}
/*
j = 11
j = 11
j = 11
j = 11
j = 11
i = 5
*/

第37课 - 变量的作用域与生命期（下）

实验—局部变量的作用域

#include <stdio.h>

int var = 1;//全局变量

void func()
{
    printf("var = %d\n", var);
}

int main()
{
    int var = 2;//局部变量1
    int i = 0;

    for(i=0; i<5; i++)
    {
        int var = 4;//局部变量2，作用域只在{}内

        var += i;

        printf("var = %d\n", var);
    }

    func();//函数调用，打印的是全局变量

    printf("var = %d\n", var);//局部变量1

    return 0;
}
/*
var = 4
var = 5
var = 6
var = 7
var = 8
var = 1
var = 2

*/

实验-变量的生命期

#include <stdio.h>

int g_var = 1;
static int g_sVar = 2;

int main()
{
    static int s_var = 3;
    auto int v = 4;
    register int rv = 5;

    printf("g_var = %d\n", g_var);//1
    printf("g_sVar = %d\n", g_sVar);//2
    printf("s_var = %d\n", s_var);//3
    printf("v     = %d\n", v);//4
    printf("rv    = %d\n", rv);//5

    return 0;
}

第38课 - 函数专题练习

编译通过，有警告，编译器默认为int
B
如果改成int func(float var){var+=1;} ,返回随机值

C

x=5,y=8, 13+7
B
搞错了z–是先取值，再减一
C 13+8

A

A

12
15

8 10

4

DELPHI TANG

#include <stdio.h>

int getNumber(char c)//字符转换为数字
{
    int ret = -1;

    if( ('0' <= c) && (c <= '9') )
        ret = c - '0';

    return ret;
}

int str2int(char str[])
{
    int ret = 0;
    int sign = 0;
    int i = 0;//首个数字的位置

    if( getNumber(str[0]) != -1 )//是数字 符号为＋
    {
        sign = 1;
        i = 0;
    }
    else if( str[0] == '+' )//
    {
        sign = 1;
        i = 1;
    }
    else if( str[0] == '-' )
    {
        sign = -1;
        i = 1;
    }

    while( sign && str[i] )
    {
        int n = getNumber(str[i]);

        if( n != -1 )
            ret = ret * 10 + n;
        else
            break;

        i++;
    }

    ret = sign * ret;

    return ret;
}

int main()
{
    printf("%d\n", str2int("123"));
    printf("%d\n", str2int("-12345"));
    printf("%d\n", str2int("567xyz89"));
    printf("%d\n", str2int("abc"));
    printf("%d\n", str2int("-xyz"));

    return 0;
}

第39课 - 递归函数简介

实验

#include <stdio.h>

int sum(int n)
{
    int ret = 0;

    if( n == 1 )
        ret = 1;
    else
        ret = n + sum(n-1);

    return ret;
}

int fac(int n)
{
    int ret = 0;

    if( n == 1 )
        ret = 1;
    else if( n == 2 )
        ret = 1;
    else if( n >= 3 )
        ret = fac(n-1) + fac(n-2);
    else
        ret = -1;

    return ret;
}

int main()
{
    int i = 0;

    printf("sum(1) = %d\n", sum(1));
    printf("sum(10) = %d\n", sum(10));
    printf("sum(100) = %d\n", sum(100));

    for(i=1; i<=10; i++)
    {
        printf("%d, ", fac(i));
    }

    printf("\n");

    return 0;
}

小结

第40课 - C 语言中的宏定义

实验

#include <stdio.h>

#define ADD(a, b) a + b

#define SWAP(a, b)  {int t = a; a = b; b = t;}

#define MIN(a, b) (a < b ? a : b)

void swap(int a, int b)
{
    int t = 0;

    // printf("a = %d, b = %d\n", a, b);

    t = a;
    a = b;
    b = t;

    // printf("a = %d, b = %d\n", a, b);

}

int main()
{
    int x = 1;
    int y = 2;

    printf("x = %d, y = %d\n", x, y);

    SWAP(x, y);   // {int t = x; x = y; y = t;}

    printf("x = %d, y = %d\n", x, y);

    printf("x + y = %d\n", ADD(x, y));

    printf("MIN(%d, %d) = %d\n", x, y, MIN(x, y));  // printf("MIN(%d, %d) = %d\n", x, y, (x < y ? x : y));

    return 0;
}

小结