Abstraction in C++ refers to the concept of hiding the complicated reality of an object while only exposing operations relevant for that object. This allows for simplifying complex systems by breaking them down into smaller, more manageable parts, enabling developers to focus on high-level functionalities.

When a class is frequently copied or assigned, it's crucial to consider the efficiency of these operations. Move semantics, introduced in C++11, allow resources to be "moved" from one object to another, without making a copy. This can greatly improve performance. Shallow copy can lead to issues like double deletion, and avoiding constructors or only using private members doesn't address the efficiency of copying or assignment.

The loop while(true) will continue to execute indefinitely since the condition is always true. This can potentially lead to an infinite loop, consuming CPU resources, and making the program unresponsive unless externally interrupted.

In C++11's range-based for loop, the const keyword ensures that elements are not modified, effectively preventing unintentional copies or modifications to the elements.

In C++, to declare a function that returns an integer, the correct syntax is "int functionName()". The type "int" signifies that the function's return type is an integer, and the parentheses "()" indicate it's a function declaration. Actual implementation or body of the function would follow the declaration.

In C++, most of the operators can be overloaded with a few exceptions. Among the operators that cannot be overloaded are: the scope resolution operator ::, the member selection operators . and .*, and the ternary conditional operator ?:.

Passing by pointer often conserves memory because only the address of the variable (usually 4 or 8 bytes, depending on the architecture) is passed, regardless of the size of the actual data. While pass by value creates a copy of the actual data, which can consume more memory, especially for large objects or structs. Pass by reference behaves similarly to pass by pointer in this regard.

Template metaprogramming (TMP) shifts computations to the compile-time, making the generated code more optimized. This results in increased compile times because the computations and code generation are happening at that phase. However, at runtime, the program may run faster or at least not have an added overhead from TMP since the computations were already done during compilation.

RSA (Rivest-Shamir-Adleman) is an encryption technique that uses two interdependent cryptographic keys, a public key for encryption and a private key for decryption. This method ensures secure communication and data protection.

Digital certificates are issued by trusted third parties known as Certificate Authorities (CAs). These entities validate the identity of individuals, organizations, or websites and issue digital certificates, which are used to establish trust and enable secure communication on the internet.

In the digital signature process, a unique hash value is generated from the data to be signed. This hash value is then encrypted with the sender's private key to create the digital signature. The recipient can use the sender's public key to verify the signature and the integrity of the data.

Digital certificates often use the PEM (Privacy Enhanced Mail) format. This format typically includes the certificate's public key and information about the key owner. PEM is widely used for securing data through encryption and authentication processes, making it an essential part of secure communications.