C语言由浅入深理解指针

#include <stdio.h>
int main()
{
    char *a;
    short *b;
    int *c;
    long *d;
    float *e;
    double *f;
    printf("sizeof(a)=%d\n", sizeof(a));
    printf("sizeof(b)=%d\n", sizeof(b));
    printf("sizeof(c)=%d\n", sizeof(c));
    printf("sizeof(d)=%d\n", sizeof(d));
    printf("sizeof(e)=%d\n", sizeof(e));
    printf("sizeof(f)=%d\n", sizeof(f));
    return 0;
}

#include <stdio.h>
int main()
{
    int a = 100;
    int *p; // 定义一个指针变量
    p = &a; // 给指针变量赋值
    printf("a = %d, %d\n", a, *p);  // *p 等价于变量 a
    return 0;
}

#include <stdio.h>
int main()
{
    int *p1, *p2, temp, a, b;
    p1 = &a;
    p2 = &b;
    printf("请输入a,b的值：\n");
    scanf("%d %d", p1, p2); // 和之前的scanf不同，这里直接用p1p2作为写入地址。
    temp = *p1;  // 用p1指向的变量a给temp赋值
    *p1 = *p2; // 用p2指向的变量b给p1指向的变量a赋值
    *p2 = temp;  // temp给p2指向的变量b赋值
    printf("a=%d b=%d\n", a, b);
    printf("*p1=%d,*p2=%d\n", *p1, *p2);
    return 0;
}

#include <stdio.h>
int main()
{
    int a = 0x1234, b = 0x5678;  // 4个字节
    char *p1, *p2;  // char类型只能保存一个字节
    printf("%#x  %#x\n", a, b);
    p1 = (char *)&a;  // 强制类型转换
    p2 = (char *)&b;
    printf("%#x  %#x\n", *p1, *p2);
    p1++;  // 指针向上移动
    p2++;
    printf("%#x  %#x\n", *p1, *p2);
    return 0;
}

#include<stdio.h>
int main(){
    int a[5] = {0,1,2,3,4};
    int *p;
    p = a;
    // 指针指向数组a的第一个元素的首地址
    printf("a[2]=%d\n",a[2]);
    printf("p[2]=%d\n",p[2]);
    // *(a+n) <==> *(p+n) <==> a[n] <==> p[n]
    printf("*(p+2)%d\n",*(p+2));
    printf("*(a+2)%d\n",*(a+2));
    printf("p=%p\n",p);
    printf("p+2=%p\n",p+2);
    return 0;
}

#include <stdio.h>
void test1()
{
    int a[10];
    int *p, *q;
    p = a;
    q = p + 2;  // p q 间隔8个字节，意味着加一个整数最终移动的字节数与指针变量的类型也有关系
    printf("p=%p\n", p);
    printf("q=%p\n", q);
    return;
}
int main()
{
    test1();
    return 0;
}

#include <stdio.h>
void test2()
{
    int a[10];
    int *p, *q;
    p = &a[1];
    q = &a[6];
    if (p < q)
    {
        printf("p < q\n");
    }
    else if (p > q)
    {
        printf("p > q\n");
    }
    else
    {
        printf("p = q\n");
    }
    return;
}
int main()
{
    //  test1();
    test2();
    return 0;
}

#include <stdio.h>
void test3()
{
    int a[10];
    int *p, *q;
    p = &a[0];
    q = &a[3];
    printf("%ld\n", q - p);
    return ;
}
int main()
{
    //  test1();
    //  test2();
    test3();
    return 0;
}

#include <stdio.h>
void test4()
{
    int a = 100;
    int *p, *q;
    p = &a;
    printf("a=%d %d\n", a, *p);
    q = p;
    printf("*q=%d\n", *q);
    *q = 999;
    printf("a=%d\n", a);
}
int main()
{
    //  test1();
    //  test2();
    //  test3();
    test4();
    return 0;
}