Added explanation for usage of CHECK macro in exercises

Author: Sebastien Ponce

exercises/classes/classes.cpp

@@ -35,6 +35,10 @@ class Fraction {
 
 // ADD YOUR CODE HERE
 
+// This is using the cpp, the C preprocessor to expand a bit of code
+// (the what argument) to a pair containing a string representation
+// of it and the code itself. That way, print is given a string and a
+// value where the string is the code that lead to the value
 #define CHECK(print,what) print(#what, what)
 
 unsigned int WIDTH {20};

exercises/classes/solution/classes_sol.cpp

@@ -53,6 +53,10 @@ class TestResultPrinter {
 
 };
 
+// This is using the cpp, the C preprocessor to expand a bit of code
+// (the what argument) to a pair containing a string representation
+// of it and the code itself. That way, print is given a string and a
+// value where the string is the code that lead to the value
 #define CHECK(printer,what) printer.process(#what, what)
 
 int main() {

exercises/operators/operators.cpp

@@ -58,6 +58,10 @@ class TestResultPrinter {
 
 };
 
+// This is using the cpp, the C preprocessor to expand a bit of code
+// (the what argument) to a pair containing a string representation
+// of it and the code itself. That way, print is given a string and a
+// value where the string is the code that lead to the value
 #define CHECK(printer,what) printer.process(#what, what)
 
 int main() {

exercises/operators/solution/operators_sol.cpp

@@ -69,6 +69,10 @@ class TestResultPrinter {
 
 };
 
+// This is using the cpp, the C preprocessor to expand a bit of code
+// (the what argument) to a pair containing a string representation
+// of it and the code itself. That way, print is given a string and a
+// value where the string is the code that lead to the value
 #define CHECK(printer,what) printer(#what, what)
 
 int main() {