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ry remains allocated for the duration of the program's execution). By default, local variables have automatic lifetime (memory is allocated and deallocated at block entry and block exit). A local variable may be given static lifetime by using the word static in its declaration. This variable has the lifetime of a global variable but the scope of a local variable. |
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C++ allows a variable to be initialized in its declaration. For a static variable, the initialization occurs once onlywhen control first reaches its declaration. An automatic variable is initialized each time control reaches the declaration. |
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C++ provides two kinds of subprograms, void functions and valuereturning functions, for us to use. A value-returning function is called from within an expression and returns a single result that is used in the evaluation of the expression. For the function value to be returned, the last statement executed by the function must be a return statement containing an expression of the appropriate data type. |
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All the scope rules, as well as the rules about reference and value parameters, apply to both void functions and value-returning functions. It is considered poor programming practice, however, to use reference parameters in a value-returning function declaration. Doing so increases the potential for side effects. (An exception is when I/O stream variables are passed as parameters. Other exceptions are noted in later chapters.) |
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We can use stubs and drivers to test functions in isolation from the rest of a program. They are particularly useful in the context of team-programming projects. |
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1. a. How can you tell if a variable that is referenced inside a function is local or global? (pp. 390395) |
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b. Where are local variables declared? (pp. 390395) |
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c. When does the scope of an identifier declared in block A exclude a block nested within block A? (pp. 390395) |
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2. A program consists of two functions, main and DoCalc. A variable x is declared outside both functions. DoCalc declares two variables, a and b, within its body; b is declared as static. In what function(s) are each of a, b, and x visible, and what is the lifetime of each variable? (pp. 390395, 397398) |
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3. Why should you use value parameters whenever possible? Why should you avoid the use of global variables? (pp. 400404, 415416) |
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4. For each of the following, decide whether a value-returning function or a void function is the most appropriate implementation. (pp. 404417) |
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a. Selecting the larger of two values for further processing in an expression. |
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b. Printing a paycheck. |
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c. Computing the area of a hexagon. |
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d. Testing whether an incoming value is valid and returning TRUE if it is. |
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e. Computing the two roots of a quadratic equation. |
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