# Lesson # 3. Arguments by Reference

Дата изменения: 24 сентября 2021

## Theory

The for loop allows you to use several counters: the initialization and increment sections can contain several operators separated by the «,» (comma) operator

 int a = 0, b = 0; for (a = 1, b = 8; a < b; ++a, --b) { // empty body } cout << a << " " << b << endl; // output 5 4

### References

References are not objects; they do not necessarily occupy storage; references are the other name of the variable:
sample 1:

 int i = 5; int &pi = i; // reference to i   pi = 3; cout << i; // i == 3

sample 2:

 void double_numb(int &numb) { numb *= numb; // 'numb' is the same as main()'s 'x' } void main(){ int x = 2; double_numb(x); cout << x << '\n'; system("pause"); }

Sample 3. Passing an argument to a function by reference:

 void calcSquareAndPerimeter(double a, double b, double &S, double &P) { S = a * b; P = 2 * (a + b); }   int main() { double SS = 0.0, PP = 0.0; calcSquareAndPerimeter(3.0, 4.0, SS, PP); cout << "Perimeter: " << PP << ", Square: " << SS << "\n"; }

All the tasks that you did not have time to complete in class automatically become your homework. The homework must be completed before the next lesson.
• Create an empty application with a name Lesson_3. All the tasks and labs must be done within this application.
• It means that all tasks must be done within the same header and source files. But you should put comments with the task number and explanation of what to do.
• Every task has to be done using user functions. For example, if the task is to find the sum of a sequence of 5 entered numbers, you must create a function within .cpp file to do this task:

 1 2 3 4 5 6 #ifndef HEADER_H #define HEADER_H // task 1 // function to calculate the sum of 5 enterered numbers int sumSeq(); #endif

imp.cpp:

 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 #include #include "header.h" using namespace std;   // function to calculate the sum of 5 enterered numbers int sumSeq() { cout << "enter a sequence"<> numb; sum += numb; } return sum; }

main.cpp:

 1 2 3 4 5 6 7 8 9 10 11 #include "header.h" #include using namespace std; void main(){ // task # 1 // craeate a function to calculate a sum of 5 entered numbers int result = sumSeq(); cout << "task 1" << endl; cout << result; system("pause"); }
• Try to pass arguments of the functions by reference (in the tasks where it is needed).
For loop:

To do: Create a function to output the sequence: -3 0 3 6 9 12 15 18 21 24. Make the task with FOR loop. An iterator of the loop has a step equaled 3.

Note 1: To make a step equal to 3 see syntax:

for ([initializers]; [condition]; [iterator])

instead of the iterator you’ll have the variable counter += 3

Note 2: The signature of the function must be void printSeq(int & a, int & b), where a = -3 and b = 24.

Note 3: Don’t forget to use assert statement to check if the boundary b is greater than a.

 #include

Expected output:

The sequence: -3 0 3 6 9 12 15 18 21 24

[Solution and Project name: Lesson_3 files: header.h, imp.cpp, main.cpp]

To do: 10 integers are entered. Create a function (findPosNeg) to output the quantity of positive and negative among them.

Note 1: Create for loop to input the numbers (they must be entered). Within the loop, check each number whether it is positive or negative. Use two counters for calculations.

Note 2: The signature of the function must be:

 void findPosNeg(int & pos, int & neg){ //TODO }

Expected output:

enter 10 numbers:
1  -5  -12   2   3   9   -1  9   5   -8
counter_positive = 6, counter_negative = 4

[Solution and Project name: Lesson_3 ]

To do: Create a function to calculate the addition of the following sequence: 1 + 3 + 5 + 7 + 9 + 11 + 13 + 15 + 17 + 19 (numbers are NOT entered, they must be created using a loop). The first number (1) and last number (19) of the sequence must be parameters of the function passed by reference.

Note: To calculate the addition, use a variable named sum.

Expected output:

the sequence:
1 + 3 + 5 + 7 + 9 + 11 + 13 + 15 + 17 + 19
sum = 100

[Solution and Project name: Lesson_3 ]

To do: For each x changing in the interval [x1;x2] (x1 and x2 values are entered), calculate the value of the function z(x,y) = xy. The variable y changes in the interval [y1;y2] (y1 and y2 values are entered). You must create a function.

Note 1: Create two for loops (nested loop): one loop within the other. Variable x has to be modified in the outer loop; variable y has to be modified in the inner loop.

Note 2: To output the power of a number, use pow function and #include<cmath> directive:

 f = pow(base number, exponent);

Note 3: Don’t forget to use the assert statement to check the boundaries (x2>x1 and y2>y1).

Expected output:

enter x1 and x2:
>>>2 >>>8
enter y1 and y2:
>>>2 >>>4
z(x,y) = 2^2 = 4
z(x,y) = 2^3 = 8
z(x,y) = 2^4 = 16
z(x,y) = 3^2 = 9
z(x,y) = 3^3 = 27
z(x,y) = 3^4 = 81
z(x,y) = 4^2 = 16
z(x,y) = 4^3 = 64
z(x,y) = 4^4 = 256
z(x,y) = 5^2 = 25
z(x,y) = 5^3 = 125
z(x,y) = 5^4 = 625
... etc.

[Solution and Project name: Lesson_3 ]

While loop:

To do: Create a function to output the sequence 15 12 9 6 3 0 (from 15 down to 0 with a step = -3). Use while loop.

Note: The signature of the function must be:

 void printSeqTask5(int & a, int & b){ … }

Where a = 15 and b = 0

Expected output:

the sequence:
15 12 9 6 3 0

[Solution and Project name: Lesson_3 ]

To do: Create a function to calculate a multiplication of 2-digit even integers in the interval [10;20] (10 * 12 * 14 * 16 * 18 * 20). You have to do the task using a while loop.

Note 1: To calculate a multiplication you should use a variable with the name product. Don’t forget to inisialize the product variable with 1.

Note 2: The signature of the function must be:

 void findMult(int & a, int & b, int & prod){ … }

where a = 10 and b = 20

Expected output:

10 * 12 * 14 * 16 * 18 * 20
the product: 9676800

[Solution and Project name: Lesson_3 ]

To do: Two two-digit integers are entered. Create a BitwiseSum() function that computes their bitwise sum modulo 10. For example, the bitwise sum of the numbers 34 and 59 is the number 83 (3 + 5 = 8; 4 + 9 = 13; 13%10 = 3).

Note: The BitwiseSum() method must accept three integers as arguments passed by reference (two numbers and sum).

Expected output:

>>> 34   >>> 59
The bitwise sum of 34 and 59 is: 83

[Solution and Project name: Lesson_3 ]

To do: A sequence of integers is given (it is entered). The last element of the sequence is 0. Calculate the addition of all positive elements of this sequence and the number of its negative elements. While loop must be used.

Note 1: In the task, you should use the endless loop with an exit from the middle:

 while (true) { // TODO something if (num == 0) break;   // TODO something }

Note 2: To return two values from the function you should use function parameters by reference (&):

 void sumPosCountNeg(int & pos_sum, int & neg) {}

Expected output:

Please enter the sequence, the last element is 0:
>>> 3   5   -1   2  -3   0
The sum of positive numbers is: 10
The number of negatives is: 2

[Solution and Project name: Lesson_3 ]

To do: A sequence of integers is given (it is entered). The last element of the sequence is 0. Find minimum and maximum elements. A While loop must be used.

Note 1: In the task, you should use the endless loop with an exit from the middle:

 while (true) { // TODO something if (num == 0) break; // TODO something // }

Note 2: To return two values from the function you should use function parameters by reference (&):

 void minMax(int &min, int &max) {}

Note 3: You should use INT32_MAX and INT32_MIN initial values for min and max variables.

Expected output:

Please enter the sequence, the last element is 0:
>>> 3   5   -1   2  -3   0
The minimum is: -3
The maximum is: 5

[Solution and Project name: Lesson_3 ]

To do: An integer is given. Find the number of its digits and their sum.

Note: The function signature should look like this:

 void digitsCountAndSum (int n, int& count, int& sum)

Expected output:

Enter number:
>>> 12345
The number of digits = 5, the sum = 15

ExtraTask 2 (passing parameters by reference):

To do: An integer N and a set of N positive real numbers are given. Calculate the sum of all integer parts, as well as the sum of all fractional parts of the sequence. Some of the standard header functions may be helpful.

Expected output:

Enter N:
>>> 4
12,4  11,7  8,5  1,1
Sum of integer parts is: 32
Sum of fractional parts is: 1.7

For loop

To do: 10 real numbers are input. Create a function to output the multiplication of the entered numbers.
Note 1: Create for loop to input the numbers. To calculate the multiplication, use a variable named product.
Note 2: Don’t forget to initialize the product variable with a double type value.

double product = 1.0;

Expected output:

1,1  2,4  5,1  7,2  6,4  8,1  6,7  3,2  3,3  2,4
product = 853338,921998746

To do: For each x changing in the interval [30;33], calculate the value of the function z(x,y) = x - y. The variable y changes in the interval [1;5]. You must create a function.

Note: Create two for loops (nested loop): one loop within the other. The variable x has to be modified in the outer loop; the variable y has to be modified in the inner loop.

Expected output:

z(x,y) = 30-1=29
z(x,y) = 30-2=28
z(x,y) = 30-3=27
z(x,y) = 30-4=26
z(x,y) = 30-5=25
z(x,y) = 31-1=30
... etc.

While loop

To do: Create a function to output the sequence 3 5 7 9 ... 21 (from 3 to 21 with a step = 2).

Note: the signature of the function must be void seq(int & a, int & b), where a = 3 and b = 21.

Expected output:

3 5 7 9 11 13 15 17 19 21

To do: 5 real numbers are input. Create a function to calculate an addition (sum) of entered numbers. Make the task using a while loop.

Note: Double type must be used for real numbers and for variable sum:

double sum = 0;
double numb;

Please enter 5 numbers and press Enter

1.1 4.2 2.1 9.3 2.5
The sum of inputted numbers = 19.2

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