为什么这一段代码用codeblocks运行会有错误？

#includeusing namespace std;
int add(int a,int b)
{
return a+b;
}
double add(double c,double d) //重载
{
return c+d;
}

char * add(char *e , char *f) //字符串连接使用strcat函数

{
strcat(e,f);
return e;
}

int main()
{
int a,b;
double c,d;
char e[100],f[100];
cin>>a>>b>>c>>d>>e>>f;
cout<<add(a,b)<<endl;
cout<<add(c,d)<<endl;
cout<<add(e,f)<<endl;
return 0;
}

错误是这样的:C:\Users\asus\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\CodeBlocks\211.c++.cpp||In function 'char* add(char*, char*)':|
C:\Users\asus\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\CodeBlocks\211.c++.cpp|16|error: 'strcat' was not declared in this scope|
||=== Build failed: 1 error(s), 0 warning(s) (0 minute(s), 0 second(s)) ===|

仔细看你编译时候的错误:

error: 'strcat' was not declared in this scope

函数strcat需要 string.h 的头文件.

在你代码前面include:

#include <string.h>