C几道小题

#include<stdio.h>

int Swap(int* x,int* y)//形参
{
    int temp;
    temp=*x;
    *x=*y;
    *y=temp;
}

int main()
{
    int a,b;
    printf("Please enter two numbers:");
    scanf("%d %d",&a,&b);
    Swap(&a,&b);//实参
    printf("a=%d b=%d\n",a,b);
    return 0;
}

#include<stdio.h>

#include<assert.h>
char  *my_strcpy(char *dst,char const *src)
{
    char *ret=dst;//为了实现链式操作，将目的地址返回
    assert(dst);
    assert(src);//对源地址和目的地址加非空断言
    if(dst==src)
        return dst;//源目所指区域重叠，直接返回目的地址
    while(*dst !='\0')
    {
        *dst=*src;
        dst++;
        src++;
    }
    /*可优化为：
    while(*dst++=*src++)
    {
        NULL;
    }*/
    return ret;
}
int main()
{    char arr[]="you are the worst";
    char *a="you are the best";
    printf("%s\n",my_strcpy(arr,a));
    getchar();
    return 0;
}

#include<stdio.h>
int my_strlen(char const *str)
{
    char const *tmp=str;
    while(*str !='\0')
    {
        str++;
    }
    return str-tmp;
}
int main() {
    char arr[30] = "trouble is a friend.";
    printf("%d\n", my_strlen(arr));
    getchar();
    return 0;
}

#include<stdio.h>
#include<string.h>
int main()
{
    char str[100];
    scanf("%s",str);
    int len;
    len=strlen(str);
    int fuction(char *, int);
    fuction(str,len);
    return 0;
}

int fuction(char *s, int n)
{
    int i;
    for(i=n-1;i>=0;i--)
        printf("%c",s[i]);
    printf("\n");
    return 1; //题目中并未提出对返回值的要求，随便输出1
}

解2：用指针

int fuction(char *s, int n)
{
    char *p;
    for(p=s+n-1;p>=s;p--)
        printf("%c",*p);
    printf("\n");
    return 1; //题目中并未提出对返回值的要求，随便输出1
}

#include <stdio.h>
#include <string.h>
void reverse(char s[])
{
    int i, j, len = strlen(s);
    char t;
    for (i = 0, j = len - 1; i < len / 2; i++, j--)
    {
        t = s[i];
        s[i] = s[j];
        s[j] = t;
    }
}
int main()
{
    char s[50];
    printf("input string:\n");
    gets(s);
    reverse(s);
    printf("after reverse:\n");
    puts(s); //注意：题目要求需在主函数中输入和输出字符串
    return 0;
}
也是反序输出