Value returned type And Void Function
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Functions
Functions
Called modules Like miniature programs Can be put together to form a larger program Two types: Predefined and User defined function
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Functions (continued)
Properties that form the function definition:
1. Name of the function 2. Number of parameters 3. Data type of each parameter 4. Type of the function 5. Code required to accomplish the task (the body of the function)
For predefined functions, you need to be concerned only with the first four properties For user defined functions, you need to be concerned with the five properties.
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Predefined Functions
Predefined functions are organized into separate libraries Some of the predefined mathematical functions are:
sqrt(x) pow(x,y)
I/O functions are in iostream/ stdio header Math functions are in cmath header
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The Power Function (pow)
pow(x,y) calculates xy, pow(2,3) = 8.0 p ( y) p ( ) pow returns a value of the type double x and y are called the parameters (or arguments) of the function pow Function pow has two parameters
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The sqrt Functions
The square root function sqrt(x)
Calculates the non-negative square root of x, for x >= 0.0 sqrt(2.25) is 1.5 Type double (returned type) and has only one parameter
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User-Defined Functions
Void functions: do not have a data type Value-returning functions: have a data type
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Value-Returning Functions
Definition of the function : Five properties Heading or function header: first four properties above Formal Parameter: variable declared in the heading Body: the fifth property Ex: double larger (double x, double y) { if (x >= y) return x; else return y; } printf(" The larger is %f ", larger(3,6)); // to call the function in main or others fns
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Syntax of Value-Returning Functions
The syntax is: y
functionType functionName(formal parameter list) { statements //declarations and/or executable statements }
functionType: type of the value returned by the function
Also called the data type or the return type
Body of function in between curly braces
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Syntax of Value-Returning Functions
The syntax of the formal p y parameter list is:
dataType identifier, dataType identifier, ...
The syntax for a function call is:
functionName(actual parameter list)
Th syntax for the actual parameter list is: The t f th t l t li t i
expression or variable,expression or variable, ...
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Value-Returning Functions
double larger (double x, double y) { if (x >= y) return x; else return y; } cout<< " The larger is " <<larger(2,3) // call larger in main printf(" The larger is %f ", larger(3,6));
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Value-Returning Functions (continued)
To use a function in your program, y can y p g you call it one or several times. When a function is called, its parameters are called actual parameters. A t l Parameter: variable or expression Actual P t i bl i listed in a call to a function
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Parameters & 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 The value of the actual parameter is copied into the memory cell of its corresponding formal parameter (value parameter)
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Function Prototype
In C++ programmers customarily place the function main before all other user-defined functions. It produces compilation errors.
Solution: place the function prototype of a value returning function before any function definition including main. Function Prototype: function heading without the body of the function The syntax is:
functionType functionName (formal parameter list); double larger(double x, d bl y); d bl l (d bl double )
It is not necessary to specify the variable name in the parameter list but you must specify the data type of each parameter
double larger (double, double);
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Flow of Execution (Continued)
Execution always begins at y g
The first statement in the function main no matter where main is placed in the program
Other functions are executed only when they are called
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Flow of Execution (continued)
A value-returning function must returns a value l A function call in a program results in the execution of the body of the called function After executing the function
The value that the function returns replaces the function call statement
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The return Statement
Once the function computes the value, the function returns the value via the return statement The syntax of the return statement is:
return expression, constant value, or variable; *largest.cpp
The data type of the value that expression computes( in the return) must match the function type.
When a return statement executes
All subsequent statements are skipped
Function immediately terminates Control goes back to the caller Return statement returns only one value If the return statement contains more than one expression, only the value of the last expression is returned. When a return statement executes in the function main, the program terminates
*returnStatement.cpp
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Value-Returning Functions
Because the value returned by a valuereturning function is unique, we must: t i f ti i i t
Save the value for further calculation Use the value in some calculation Print the value
A value-returning function is used in an assignment , in an output statement, as a parameter in a function call
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Value-Returning Functions (continued)
A value-returning function is called: In an expression in the main which may be part of an assignment statement or an output statement : y=10; z= 2+y; x= 5+ larger(y,z) ; printf(Larger is %d \n, larger(y,z)); As a parameter in a function call as in compareThree: larger(x larger(y z)) larger(x, larger(y,z)) Save the value for later calculation:x= larger(y,z) Note:To execute a function call, the parameters are evaluated first.
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Value-Returning Functions
To call a value-returning function:
Use its name, with the actual parameters (if any) in parentheses In a function call, you specify only the actual p parameter, not its data type. , yp There is a one-to-one correspondence between actual and formal parameters
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void Functions
void functions and value-returning functions g 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 after main main. main, the function prototype must be placed before the function main
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void Functions (continued)
A void function does not have a data type yp The 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
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void Functions Without Parameters
Function definition syntax: y
void functionName() { statements }
void is a reserved word Function call syntax:
functionName();
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void Functions With Parameters
Function definition syntax: y
void functionName(formal parameter list) { statements }
Function call syntax:
functionName(actual parameter list);
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void Functions With value Parameters (continued)
A formal parameter ( p (value p parameter) ) 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 f th di t l t
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Value Parameters
If a formal parameter is a value p p 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
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Reference Variables as Parameters
If a formal parameter is a reference p parameter
It receives the address of the corresponding actual parameter
A reference parameter stores the address of the corresponding actual parameter
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Reference Variables as Parameters (continued)
During program execution to manipulate the data
The address stored in the reference parameter directs it to the memory space of the corresponding actual parameter
During execution, changes made by the formal parameter permanently change the value of the actual parameter
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Reference Variables as Parameters (continued)
Reference parameters are useful in three p situations:
Returning more than one value Changing the actual parameter When passing the address would save memory space and time
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Reference parameters and value returning function
You can also use reference parameters in a p value returning function. By definition a value return 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.
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