Value and Reference Parameters

CSCE 1062 Outline  Summary of value parameters  Summary of reference parameters  Argument/Parameter list correspondence (NOT)  Array elements as arguments (section 9.3)  Flowchart notation for a user defined function  Structure charts

CSCE 1063 Summary of Value Parameters  Value of corresponding actual argument is stored in the called function  The function execution cannot change the actual argument value  Actual argument can be an expression, variable, or constant  Formal parameter type must be specified in the formal parameter list  Parameters are used to store the data passed to a function

CSCE 1064 Summary of Reference Parameters  Address of corresponding actual argument is stored in the called function  The function execution can change the actual argument value  Actual argument must be a variable only  Formal parameter type must be followed by & in the formal parameter list  Parameters are used to return outputs from the function or to change the value of a function argument

CSCE 1065 Listing 6.2 Functions main and test

CSCE 1066 Argument/Parameter List Correspondence (NOT)  Number: number of actual arguments used in function call must be the same as the number of formal parameters listed in the function header and prototype  Order: Order of arguments in the lists determines correspondence  Type: Each actual argument must be of a data type that can be assigned to the corresponding formal parameter with no unexpected loss of information

CSCE 1067 Array Elements as Arguments  Exercise: Create a C++ function called “exchange” to exchange the contents of two floating-point memory locations.  Can pass array elements to functions exchange (s[3], s[5]);

CSCE 1068 A program module/function is represented in flowcharts by the following special symbol. Flowchart Function Notation

CSCE 1069 The position of the function/module symbol indicates the point the function is executed/called. A separate flowchart should be constructed for the function/module. START END Read Input Call calc_pay function Flowchart Function Notation (cont’d) Display results

CSCE Exercise 1 Draw a flowchart for an algorithm that calculates the average of two numbers by the use of a value returning function (computeAverage). The main function should input the two numbers, as well as outputting the average.

CSCE Solution INPUT n1, n2 OUTPUT average START STOP START STOP average = computeAverage(n1, n2) return (n1 +n2)/2 computeAverage main

CSCE Figure 6.4 Structure chart for general sum and average problem

CSCE // File: computeSumAve.cpp // Computes and prints the sum and average of a collection of data #include using namespace std; // Functions used... // Computes sum of data float computeSum (int);// IN - number of data items // Computes average of data float computeAve (int,// IN - number of data items float);// IN - sum of data items // Prints number of items, sum, and average void printSumAve (int,// IN - number of data items float,// IN - sum of the data float);// IN - average of the data Listing 6.6 main function

CSCE int main( ) { int numItems;// input - number of items to be added float sum;// output - accumulated sum of the data float average;// output - average of data being processed // Read the number of items to process. cout << “Enter the number of itesm to process: “; cin >> numItems; // Compute the sum of the data. sum = computeSum(numItems); // Compute the average of the data. average = computeAve(numItems, sum); // Print the sum and the average. printSumAve(numItems, sum, average); return 0; } Listing 6.6 main function (continued)

CSCE Listing 6.7 Function computeSum // Computes sum of data. // Pre: numItems is assigned a value. // Post: numItems data items read; their sum is stored in sum // Returns: Sum of all data items read if numItems >= 1; //otherwise, 0; float computeSum (int numItems) // IN: number of data items { // Local data... float item;// input: contains current data item float sum;// output: used to accumulate sum of data //read in

CSCE Listing 6.7 Function computeSum (continued) // Read each data item and accumulate it in sum. sum = 0.0; for (int count = 0; count < numItems; count++) { cout << “Enter a number to be added: “; cin >> item; sum += item; } // end for return sum; } // end computeSum

CSCE Listing 6.8 Function computeAve // Computes average of data // Pre: numItems and sum are defined; numItems must be // greater than 0. // Post: If numItems is positive, the average is computed // as sum / numItems. // Returns: The average if numItems is positive; //otherwise, 0; float computeAve (int numItems, // IN: number of data items float sum;// IN: sum of data

CSCE Listing 6.8 Function computeAve (continued) { // Compute the average of the data. if (numItems < 1) // test for invalid input { cout << “Invalid value for numItems = “ << numItems << endl; cout << “Average not computed.” << endl; return 0.0; // return for invalid input } return sum / numItems; } // end computeAve

CSCE Listing 6.9 Function printSumAve // Prints number of items, sum, and average of data. // Pre: numItems, sum, and average are defined. // Post: displays numItems, sum and average if numItems > 0 void printSumAve (int numItems,// IN: number of data items float sum,// IN: sum of the data float average)// IN: average of the data

CSCE Listing 6.9 Function printSumAve (continued) { // Display results is numItems is valid. if (numItems > 0) { cout << “The number of items is “ << numItems << endl; cout << “The sum of the data is “ << sum << endl; cout << “The average of the data is “ << average << endl; } else { cout << “Invalid number of items = “ << numItems << endl; cout << “Sum and average are not defined.“ << endl; cout << “No printing done. Execution terminated.” << endl; } // end if } // end printSumAve

CSCE The following formula gives the distance between two points (x1, y1) and (x2, y2) in the Cartesian plane: (x2 – x1) 2 + (y2 – y1) 2 ) Given the centre and a point on the circle, you can use this formula to find the radius of the circle. Draw the flow charts and write a complete C++ program that prompts the user to enter the centre and a point on the circle. The program should then compute and output the circle's radius, diameter, circumference, and area. Your program must have at least the following user-defined functions:  Distance. This function takes as its parameters four numbers that represent two points in the plane and returns the distance between them.  Radius. This function takes as its parameters four numbers that represent the center and a point on the circle, calls the function Distance to find the radius of the circle, and returns the circle's radius.  Circumference. This function takes as its parameters a number that represents the radius of the circle and returns the circle's circumference. (If r is the radius, the circumference is 2  r)  Area. This function takes as its parameters a number that represents the radius of the circle and returns the circle's area. ((If r is the radius, the area is  r 2 )  Assume  = Please use a structure chart to help you analyse the given exercise. Exercise 2

CSCE Next lecture will be about Arrays as Function Parameters