C++ Primer Section 1-3

Contents and Thoughts

Two kinds of comment

There are two kinds of comment in C++, single-line and paired(in CommentsInAddTwoNumbers.cpp).

• Single-line. Start with // and end with a newline

• Paired: Start with /* and end with */

Paired Comments NO NEST

Paired Comments do not nest. So there should not be another paired comment in a paired comment(like in PairNoNest.cpp).

Way to ignore blocks when debugging or re-editing the code

As paired comments do not nest, re-editing code with paired comment is a bad idea. You never know where there may be another paired comment, which leads to nested comments.
An feasible way is to turn every line into a single-line comment(like in OneLineToGo.cpp).

Exercise

Exercise 1-7

Compile a program that has incorrectly nested comments.

Solution

Compile PairNoNest.cpp and get this

PairsNoNest.cpp:2:28: error: ‘cannot’ does not name a type

• comment pairs /* */ cannot nest.

Exercise 1-8

Indicate which, if any, of the following output statements are legal:

std::cout << "/*";
std::cout << "*/";
std::cout << /* "*/" */;
std::cout << /* "*/" /* "*/" */;

After you’ve predicted what will happen, test your answers by compiling a program with each of these statements. Correct any errors you encounter.

Solution

The *i*th line of code is in the file 1-8-i.cpp in Exercise Code

The 1st, 2nd and 4th lines are all legal. But line 3rd is illegal. Compiling 1-8-3.cpp will produce

1-8-3.cpp:5:21: warning: missing terminating ” character
std::cout << /* “/” /;
^
1-8-3.cpp:5:2: error: missing terminating ” character
std::cout << /* “/” /;
^
1-8-3.cpp: In function ‘int main()’:
1-8-3.cpp:6:2: error: expected primary-expression before ‘return’
return 0;
^

Adjusting 3rd tostd::out << /* "*//*" */;does not work, indicating that << must have an operant in the right-hand side.

But adjusting it to std::cout << /* "*/""/**/; works well(in 1-3-8-Correction.cpp), though it does nothing.