Chapter 1 C++: Function return values, GNU compiler commands

Function return value

• The return value type must be the same as the return type of the function

• For the main function, the return value must be of type int. On most systems, the return value of the main function is a status indicator. A return value of 0 indicates that the main function has been executed successfully; a return value of non-zero indicates that an error occurred.

GNU compiler commands

• vi: New file, i: Edit; Esc Exit editing; wq/ZZ: Save and exit

• g XX.cc -o XX: Compile XX.cc and generate executable file XX.

  ./XX: Run the executable file XX

• echo $?: After executing the program, access the return value of the main function to obtain the status.

Input and output iostream

iostream library, input stream (istream) and output stream (ostream)

• Standard input: cin

• Standard output: cout

• cerr: Standard error, used to output program warning and error messages.

• clog: used to generate general information about program execution.

1. Preprocessing instructions: #include

2. Write to stream

• Output operator :<<, each output operator instance accepts two operands, the left operand must be an ostream object, and the right operand is the value to be output.

• Manipulator (manipulator) endl: writes it to the output stream, has the effect of line wrapping output, and refreshes the buffer associated with the device so that the user can view it immediately to write the output to the stream.

3. Use the names in the standard library, such as std::cout, std::endle

• means that cout and endl are defined inNamespace(namespace)

• Scope operator (scope operator, ::operator)

4. Read the stream, such as std::cin >> v1 >> v2;

• Input operator:>>

5. Comments

• Comment delimiters (/**/) cannot be nested

• Best when commenting code snippets Use single-line comments (//)

Read an unknown number of inputs

• Sum a set of numbers specified by the user and keep reading Take until the end of input.

int val;//read until end-of-file*/while（std::cin >> val） { ......}

• Use the istream object as the condition, and the result is the status of the test stream. If the stream is valid, the test succeeds; if an end-of-file is encountered or the input is invalid (if the read is not an integer value, the istream object is invalid), the test will fail. .

• Enter the file end character from the keyboard: the file end character Ctrl D in Unix, which is equivalent to (Ctrl Z Enter)*2 in the .c file of vc in Windows. Note: EOF is not required in the code.

• The variables defined in the for loop can only exist in the for loop and cannot be used after the loop ends.

• "Edit-Compile-Debug", after correcting an error or a small part of the error, recompile the code immediately.

Class

• Standard library header files are enclosed in angle brackets <>, and non-standard library header files are enclosed in double quotes.” "Bracket it.

• Member function, also known as class method. To call member functions, use the dot operator (.).

• Call operator: ().

Using file redirection

$ addaItems  outfile

• The addition program has been compiled into an executable file for addItems. The above command will read from a file named infile Read the records and output the results to a file named outfile.

Terms

• argument(actual parameter): The value passed to the called function

• block (block): sequence of statements enclosed in curly braces

• main function (main function): execution C program, the function called by the operating system. Each program has and has only one main function main

• manipulator (manipulator): "Manipulate" the object of the stream itself when reading or writing, such as std: :ebndl.

• member function (member function), method (method): synonyms, referring to the operations defined by the class

• Namespace (namespace): A mechanism to put the names defined by the library into a single place. Namespaces help avoid unintentional naming conflicts. Names defined by the C standard library are in the namespace std.

• string literal: A sequence of characters enclosed in double quotes

• Uninitialized variable (uninitialized variable): If the class type does not specify an initial value, it will be initialized according to the class definition. Built-in type variables defined inside a function are not initialized by default unless there is an explicit initialization statement.

Reference: C Primer Fifth Edition

Related articles:

Chapter 2 C: Variables and Basic Types

Chapter 3 C: string string, vector vector and array

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