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cs31 lecture 4

Called inferred x examples int foo 2 float bar 32

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Unformatted text preview: port all basic types as rhs float, double, int, char, … Also with qualifier x The user doesn’t need to specify the type of the rhs, it is The inferred by the compiler and the good << operator is called inferred x Examples: int foo = 2; float bar = 3.2; std::cout << “foo is: “ << foo << “ and bar is: “ << bar << std::endl; std::cout 11 Some observations x Variables and more generally expressions can be printed Variables out out x For floating point values, not all digits are printed out There are commands to set the precision It doesn’t mean the number has been truncated x For complex, user-defined types, must define the operator For << << 12 Console input x Useful to get some input from the user, through the Useful keyboard (usually) keyboard x Principle: “push” the standard input into a variable x Example: int foo; std::cin >> foo; float bar; float std::cin >> bar; std::cin 13 Some observations x “Conversion” happens when the input does not match the Conversion” type type Example: int foo; std::cin >> foo; std::cout << foo << std::endl; Giving 123.45 as input on the keyboard leads to printing 123 x If the input is “meaningless”, then no assignment is If performed performed Example: input “foo” to the above program leaves the value of foo Example: unchanged unchanged 14 Complete example 15 Control structure: if-then-else x Syntax in C++: IIf (<condition>) f <instructions1> <instructions1> [else [else <instructions2>] <instructions2>] x Instructions are usually a block, that is { … } x <condition> is an expression When it evaluates to 0 or ‘false’, then <instructions1> is not When executed, and if there is a else, then <instructions2> is executed executed, When it evaluates to any value not 0, or ‘true’, then <instructions1> When is executed is 16 More on conditions x Can use standard operators for comparison of values < or > or <= or >= or == Be careful: = is assignment, == is comparison 12 < 12 is a false expression 12 < 13 is a true expression 12 is a non-0 expression (hence “true”) x Conjunction/disjunction can be expressed with logical Conjunction/disjunction operators operators && for logical and || for logical or 17 Complete example 2 18...
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