Calculate the sum of interior angles of a polygon
The most serious problem I see here is failing to check the return value from scanf().  Never ignore that - it's the only way we have to determine whether conversions were successful.

A less serious issue is that we we're using a main() that takes command-line arguments, but never use them.  Prefer instead the no-argument version:

int main(void)


The copying of the shape's name isn't useful - we can just pass the pointer directly to printf():

        printf("The sum of the interior angles of a %s is %i\n",
               names[numSides - 3],
               getSumInteriorAngles(numSides));


We could even choose which to print by using a suitable pointer:

const char* names[] = {
    "a triangle",
    "a quadrilateral",
    "a pentagon",
    "a hexagon",
    "a heptagon",
    "an octagon",
    "a nonagon",
    "a decagon",
    "a hendecagon",
    "a dodecagon"
};

// ...

const char *name = "this polygon";
if (numSides &lt;= 12) {
    name = names[numSides - 3];
}

printf("The sum of the interior angles of %s is %i\n",
       name, getSumInteriorAngles(numSides));


This also stops the code printing the ungrammatical "a octagon". :-)