4. Write your own string concatenation function with signature: void string_cat(char * leftPtr, char * rightPtr) leftPtr and rightPtr are null terminated strings. rightPtr will be copied into leftPtr starting at leftPtr's null terminator (overwriting it). Make sure your leftPtr is null terminated when complete. Use the following test code: void test_string_cat() { char left [] = "Hello"; char right [] = "World"; char concat [20]; concat[0] = '\0'; string_cat(concat, left); string_cat(concat," "); string_cat(concat, right); printf("%s ", concat); }