C++数组维度提示不是常量，是按照教科书编程的，是不是编译器的原因。

#include
#include
using namespace std;
int main()
{
char ch1[] = "woainidan";
char ch2[] = "iloveyou";
char result[strlen(ch1) + strlen(ch2)];
strcpy(result, ch1);
strcat(result, ch2);
cout << ch1 << " " << ch2<<" " << result << endl;
return 0;

}

char result[strlen(ch1) + strlen(ch2)];
->
char * result = new char[strlen(ch1) + strlen(ch2)];

char result[sizeof(ch1) + sizeof(ch2)];

 #include "stdafx.h"
#include <string>
#include <iostream>
int _tmain(int argc, _TCHAR* argv[])
{
    char ch1[] = "woainidan";
    char ch2[] = "iloveyou";
    char* result = new char[strlen(ch1) + strlen(ch2)];
    strcpy_s(result, strlen(ch1), ch1);
    strcat_s(result, strlen(ch2), ch2);
    std::cout << ch1 << " " << ch2<<" " << result << std::endl;
    return 0;
}

 char ch1[] = "woainidan";
    char ch2[] = "iloveyou";
    size_t isize = strlen(ch1) + strlen(ch2) + 1;
    char* result = new char[isize];
    memset(result, 0, strlen(ch1) + strlen(ch2) + 1);
    strcpy_s(result, strlen(ch1) + 1, ch1);
    strcat_s(result + strlen(ch1), isize - strlen(ch1), ch2);
    std::cout << ch1 << " " << ch2<<" " << result << std::endl;

同意一楼，但解决方法不是唯一的，一楼也许改变了原意。

char result[sizeof(ch1) + sizeof(ch2)];
因为sizeof不是函数，是个运算符，在预编译时即转为了常量