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 :36d6486cf162dff701d9668ac486e0bf> 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 a8093152e673feb7aba1828c43532094, 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 <infile> 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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