Define user defined functions

What is the use of in line function?

Write the output of the following program.
using namespace std;
#include< iostream >
#inc1ude< ctype.h >
int maint)
{
char ch = '3';
cout<< "\n The Return Value of isdigit(ch) is :" <<
isdigit( ch) ;
}

Write the output of the following program.
#include < string.h >
#include < iostream >
using namespace std;
int main()
{
char target[50] = "Learning C++ is fun";
char source[50] =" , easy and Very useful";
strcat(target, source);
cout << target;
return 0;
}

What are the advantages of inline functions?