University:
Kentucky State University
Course:
COS 232| Programming I
Academic year:

2019
Views:

440

Pages:

38
Author:

Arielle Armstrong

Chapter 7: User-Defined Functions II Objectives In this chapter, you will: • Learn how to construct and use void functions in a program • Discover the difference between value and reference parameters • Explore reference parameters and valuereturning functions • Learn about the scope of an identifier 2 Objectives (continued) • Examine the difference between local and global identifiers • Discover static variables • Learn function overloading • Explore functions with default parameters 3 Void Functions • Void functions and value-returning functions have similar structures − Both have a heading part and a statement part • User-defined void functions can be placed either before or after the function main • If user-defined void functions are placed after the function main − The function prototype must be placed before the function main 4 Void Functions (continued) • A void function does not have a return type − return statement without any value is typically used to exit the function early • Formal parameters are optional • A call to a void function is a stand-alone statement 5 Void Functions without Parameters • Function definition syntax: • void is a reserved word • Function call syntax: 6 Void Functions with Parameters • Function definition syntax: • Formal parameter list syntax: • Function call syntax: • Actual parameter list syntax: 7 Void Functions with Parameters (continued) 8 Void Functions with Parameters (continued) • Value parameter: a formal parameter that receives a copy of the content of corresponding actual parameter • Reference parameter: a formal parameter that receives the location (memory address) of the corresponding actual parameter 9 Value Parameters • If a formal parameter is a value parameter − The value of the corresponding actual parameter is copied into it • The value parameter has its own copy of the data • During program execution − The value parameter manipulates the data stored in its own memory space 10 Reference Variables as Parameters • If a formal parameter is a reference parameter − It receives the memory address of the corresponding actual parameter • A reference parameter stores the address of the corresponding actual parameter • During program execution to manipulate data − The address stored in the reference parameter directs it to the memory space of the corresponding actual parameter 11 Reference Variables as Parameters (continued) • Reference parameters can: − Pass one or more values from a function − Change the value of the actual parameter • Reference parameters are useful in three situations: − Returning more than one value − Changing the actual parameter − When passing the address would save memory space and time 12 Calculate Grade 13 Calculate Grade (continued) 14 Value and Reference Parameters and Memory Allocation • When a function is called − Memory for its formal parameters and variables declared in the body of the function (called local variables) is allocated in the function data area • In the case of a value parameter − The value of the actual parameter is copied into the memory cell of its corresponding formal parameter 16 Value and Reference Parameters and Memory Allocation (continued) • In the case of a reference parameter − The address of the actual parameter passes to the formal parameter • Content of formal parameter is an address • During execution, changes made by the formal parameter permanently change the value of the actual parameter • Stream variables (e.g., ifstream) should be passed by reference to a function 17 Reference Parameters and ValueReturning Functions • You can also use reference parameters in a value-returning function − Not recommended • By definition, a value-returning function returns a single value − This value is returned via the return statement • If a function needs to return more than one value, you should change it to a void function and use the appropriate reference parameters to return the values 25 Scope of an Identifier • The scope of an identifier refers to where in the program an identifier is accessible • Local identifier: identifiers declared within a function (or block) • Global identifier: identifiers declared outside of every function definition • C++ does not allow nested functions − The definition of one function cannot be included in the body of another function 26 Scope of an Identifier (continued) • Some compilers initialize global variables to default values • The operator :: is called the scope resolution operator • By using the scope resolution operator − A global variable declared before the definition of a function (block) can be accessed by the function (or block) even if the function (or block) has an identifier with the same name as the variable 28 Scope of an Identifier (continued) • C++ provides a way to access a global variable declared after the definition of a function − In this case, the function must not contain any identifier with the same name as the global variable 29 Global Variables, Named Constants, and Side Effects • Using global variables has side effects • A function that uses global variables is not independent • If more than one function uses the same global variable and something goes wrong − It is difficult to find what went wrong and where − Problems caused in one area of the program may appear to be from another area • Global named constants have no side effects 30 Function Overloading: An Introduction • In a C++ program, several functions can have the same name − This is called function overloading or overloading a function name 31 Function Overloading (continued) • Two functions are said to have different formal parameter lists if both functions have: − A different number of formal parameters, or − If the number of formal parameters is the same, then the data type of the formal parameters, in the order you list them, must differ in at least one position 32 Function Overloading (continued) • The following functions all have different formal parameter lists: • The following functions have the same formal parameter list: 33 Function Overloading (continued) • Function overloading: creating several functions with the same name • The signature of a function consists of the function name and its formal parameter list • Two functions have different signatures if they have either different names or different formal parameter lists • Note that the signature of a function does not include the return type of the function 34 Function Overloading (continued) • Correct function overloading: • Syntax error: 35 Summary • Void function: does not have a data type − A return statement without any value can be used in a void function to exit it early − The heading starts with the word void − To call the function, you use the function name together with the actual parameters in a standalone statement • Two types of formal parameters: − Value parameters − Reference parameters 36 Summary (continued) • A value parameter receives a copy of its corresponding actual parameter • A reference parameter receives the memory address of its corresponding actual parameter − If a formal parameter needs to change the value of an actual parameter, you must declare this formal parameter as a reference parameter in the function heading 37 Summary (continued) • Variables declared within a function (or block) are called local variables • Variables declared outside of every function definition (and block) are global variables • Automatic variable: variable for which memory is allocated on function/block entry and deallocated on function/block exit • Static variable: memory remains allocated throughout the execution of the program • C++ functions can have default parameters 38

Chapter 7 User-Defined Functions II

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