Problem $1$:

Write a function that will search a string for any one of a given set of characters.

Your function should match this prototype:

char $*$ find$\_$char$($char const $*$source$,$ char const $*$chars$)$;

The basic idea is to locate the first character in the source string that

matches any of the characters in the chars string. The function then returns a

pointer to the place in source where the first match was found. If none of the

characters in source match any of the chars, then a NULL pointer is returned. If

either argument is NULL, or either string is empty, then a NULL pointer is returned.

To illustrate, suppose source points to ABCDEDG. If chars points to $xYZ,$ JURY,

or QQQQ$,$ the function should return NULL. If chars points to XRCQEF, the function

should return a pointer to the C in source. The strings that the arguments point to

are never modified.

As it happens, there is a function in the C library called strpbrk that behaves

almost exactly the same as the one you are to write. But the object of this program

is for you to manipulate the pointers yourself, so

a$.$ You may not use any of the library string routines $($for example, strcpy$,$ strcmp$,$

index, etc.$),$ and

b$.$ you may not use subscripts anywhere in your function.