指针复习

Posted 2020-10-06 梁锦杰

/*
 ============================================================================
 Name        : Hello.c
 Author      : 
 Version     :
 Copyright   : Your copyright notice
 Description : Hello World in C, Ansi-style
 ============================================================================
 */

#include <stdio.h>
#include <stdlib.h>
void reset(int i);
void reset2(int* p);
void add_by_point(int x,int y,int *result);
int main(void) {

    printf("%d\n",sizeof(char));
    printf("%d\n",sizeof(int));
    int a = 10;
    int *p1 = &a;
    char *p2 = p1;

    printf("%d\n",p1);
    printf("%d\n",p2);

    printf("%d\n",*p1);//10
    printf("%d\n",*p2);

    puts("----------------------");
    int c[10] = {
            1,2,3,4,5
    };
    //数组内容值默认为0
    printf("%d\n",c[5]);
    //数组名也是数字首地址
    printf("%d\n",c);
    //指针运算要根据指针的类型
    printf("%d\n",c+1);
    //
    printf("%d\n",*(c+2));
    *(c+2) = 0;
    printf("%d\n",*(c+2));

    puts("----------------------");
    int d = 10;
    reset(d);
    //函数独立性
    printf("%d\n",d);
    reset2(&d);
    //使用指针的方式突破函数壁垒
    printf("%d\n",d);

    //什么是返回值
    int e = add(3,5);
    printf("e = %d\n",e);
    int result = 0;
    //指针的方式计算结果
    add_by_point(3,5,&result);
    printf("result = %d\n",result);

}
void reset(int i){
    i = 0;
}
void reset2(int* p){
    *p = 0;
}


int add(int i,int j ){
    /*
     * 变量的生命周期
     *
     * */

    int q = i+j;
    return q;
}

void add_by_point(int x,int y,int *result){
    int r = (x + y);
    *result = r;
}