[amp_mcq option1=”add::ios” option2=”in::file” option3=”ios::app” option4=”ios::in E. ios::out” correct=”option4″]

The correct answer is: D. ios::in

The ios::in mode tells C++ to open a file for input. This means that the program can read data from the file. The other options are incorrect because they do not tell C++ to open a file for input.

• add::ios is a macro that is used to define the type of an object. It is not used to open a file.
• in::file is a type of file that can be opened in C++. However, it is not the mode that tells C++ to open a file for input.
• ios::app is a mode that tells C++ to open a file for appending. This means that the program can write data to the end of the file.
• ios::out is a mode that tells C++ to open a file for output. This means that the program can write data to the file.

Here is an example of how to open a file for input in C++:

“`c++

include

include

int main() {
std::ifstream file(“input.txt”);
if (file.is_open()) {
std::string line;
while (std::getline(file, line)) {
std::cout << line << std::endl;
}
file.close();
} else {
std::cout << “Error opening file.” << std::endl;
}
return 0;
}
“`

In this example, the file “input.txt” is opened for input. The program then reads each line from the file and prints it to the console. When the program reaches the end of the file, the file is closed.