#include<stdio.h> char *mystrcpy(char *dest,char *src); unsigned int mystrlen(char *src); char *mystrcat(char *dest,char *src); int main(int argc, const char *argv[]) { char str[20] = { 0 }; char *p = NULL; p = "hello"; char *p1 = "world"; mystrcpy(str,p); mystrcat(str,p1); puts(str); printf("len = %d ",mystrlen(str)); return 0; } unsigned int mystrlen(char *src) { char *head = src; if(src == NULL) return 0; while(*src != '