Topics Covered on Monday, 2010-08-09

• Objects in C++ may be declared or defined.
• Every object declared must also be defined somewhere.
• A declaration describes the object without actually creating it. For variables, it describes the type of the variable. For functions, it describes the return type and the arguments of the function.
• A definition actually creates the object. For variables, space is allocated. For functions, the function body is compiled.

Data Types in C++

• String constants: enclosed in "double quotes", need one extra byte of storage to terminate string with byte with value 0.
• Integer types: include int (typically 32 bits), long int (typically 64 bits), short int (typically 16 bits) and char (typically 8 bits).
  • Integers may be signed or unsigned.
  • Integers can store fixed ranges of values.
• Floating-point types: include float (typically 32 bits) and double (typically 64 bits).
  • Stored as mantissa and exponent.
  • Range is very high, but number of significant digits stored varies.

Sample program (hello.cpp)

1  // hello.cpp
2  // Print "Hello, world" on the display
3  // Copyright (C) 2010, Raj Mathur
4  #include <iostream>
5  #include <cstdlib>
6  using namespace std;
7  int main(int argc, char *argv[])
8  {
9     cout << "Hello, world" << endl;
10   exit(0);
11 }

• Line 5 is used for declarations of common functions (exit in our program).
• Lines 8 and 11 are used to begin and end the function definition.
• Line 6 is a C++ statement that applies the operator << to the object cout (which is declared in iostream). The argument to the operator is the string "Hello, world".
• After that, line 16 applies the << to the cout object again with the parameter endl. endl is a manipulator that causes a new line to be printed on the output.
• Line 10 calls the function exit (declared in cstdlib), which terminates the program and passes the argument 0 to the operating system.

Sample program (add.cpp)

1  // add.cpp
2  // Prompt user for two numbers and print out the sum.
3  // Copyright (C) 2010, Raj Mathur
4  #include <iostream>
5  #include <cstdlib>
6  using namespace std;
7  int main(int argc, char *argv[])
8  {
9    int
10     number_1;
11   int number_2, result;
12   number_1 = number_2 = result = 0;
13   cout << "What is the first number? ";
14   cin >> number_1;
15   cout << "What is the second number? ";
16   cin >> number_2;
17   result = number_1 + number_2;
18   cout << "The sum is " << result << endl;
19   exit(0);
20 }

• Lines 9 and 10 define an int variable named number_1.
• Line 12 defines two int variables named number_2 and result.
• Line 13 sets result to 0, then sets number_2 and then number_1 to the same value.
• Lines 14 and 16 read the values from the user and store them in number_1 and number_2.
• Line 17 assigns the result of the addition to the variable result.