1.  (5) Write a function that calculates the gcd of two integers.  Make the 
function recursive.  Do not use loops.  Write a main function that utilizes 
the gcd function to calculate the gcd of inputted integers.

2.  (5+5+5+5)  Write a "vector library."  This library should allow some 
operations on vectors.  Vectors are ordered sets of real numbers (i.e. arrays
of doubles).  Make sure to test your operations by writing a main function
that uses them.  Your library should provide the following 
operations (functions):
component-wise addition: <2.5, 3.2, 5.6> + <2.4, 2.3, 2.1> = <4.9, 5.5, 7.7>
void addVec(double dst[], double u[], double v[], int size);

component-wise subtraction
void subVec(double dst[], double u[], double v[], int size);

component-wise multiplication
void mulVec(double dst[], double u[], double v[], int size);

dot-product: <1.0, 2.0, 3.0> + <4.0, 5.0, 6.0> =
             1.0*4.0 + 2.0*5.0 + 3.0*6.0 = 32.0
double dotproduct(double u[], double v[], int size);


3.  (5+5)  Write a function called strcpy that takes in two strings and copies
the contents of the first string to the second string.  Write another function
called strcat, which concatenates string s1 to string s2, placing the full
string in dst.
void strcpy(char src[], char dst[]);
void strcat(char dst[], char s1[], char s2[]);