cse1222: lecture 3the ohio state university1. assignment operations the c++ assignment operator is:...

CSE1222: Lecture 3 The Ohio State University 1

Assignment Operations The C++ assignment operator is:

= Examples:

x = 3 * 5;y = x – 7;y = y + 4;

Do not confuse assignment for equality!


Assignment Operations Remember our rule:

A variable, and only one variable, must be on the leftAny expression that evaluates to the same data

type as the variable can be on the right

Example:y = x – 7;

Syntax error:x – 7 = y; // syntax error

An expression cannot appear on the left(Left and right are not interchangeable)


Expressions An expression is a combination of

constants, variables, and function calls that evaluate to a result

Example: x = 3.0 * 4.0;y = 2.0 + x;z = 5.0 + x/y - sqrt(x * 3.0);

Remember: Variables (i.e., x,) must be defined before they are used


average.cpp// Compute the average of three numbers.#include <iostream>using namespace std;

int main(){ double x1, x2, x3, sum, average;

cout << "Enter three numbers : "; cin >> x1 >> x2 >> x3;

sum = x1 + x2 + x3; average = sum / 3.0;

cout << "The average is: " << average << endl;

return 0;}


> average.exeEnter three numbers : 2.5 3.1 0.2The average is: 1.93333

>


… double x1, x2, x3, sum, average;

cout << "Enter three numbers : "; cin >> x1 >> x2 >> x3;

sum = x1 + x2 + x3; average = sum / 3.0;

cout << "The average is: " << average << endl;…

bmi.cpp// Compute the body mass index (BMI)#include <iostream>using namespace std;

int main(){ double height, weight, height_squared, bmi;

cout << "Enter height (inches): "; cin >> height; cout << "Enter weight (pounds): "; cin >> weight;

height_squared = height * height; bmi = weight * 705.0 / height_squared;

cout << "Body Mass Index = " << bmi << endl;

return 0;}


simpleslope.cpp// Compute the slope between two points#include <iostream>using namespace std;

int main(){ double x1, y1, x2, y2, xdiff, ydiff, slope;

cout << "Enter x and y coordinates of first point : "; cin >> x1 >> y1; cout << "Enter x and y coordinates of second point : "; cin >> x2 >> y2;

xdiff = x1 - x2; ydiff = y1 - y2; slope = ydiff / xdiff; cout << "The slope is: " << slope << endl;

return 0;}


> simpleslope.exe

Enter x and y coordinates of first point : 0 3

Enter x and y coordinates of second point : 4 1

The slope is: -0.5

>


… double x1, y1, x2, y2, xdiff, ydiff, slope;

cout << "Enter x and y coordinates of first point : "; cin >> x1 >> y1; cout << "Enter x and y coordinates of second point : "; cin >> x2 >> y2;

xdiff = x1 - x2; ydiff = y1 - y2; slope = ydiff / xdiff; cout << "The slope is: " << slope << endl;…

simpleslope.cpp

What is the potential problem with this code?


... xdiff = x1 - x2; ydiff = y1 - y2; slope = ydiff / xdiff; cout << "The slope is: " << slope << endl;...

Assignment Variations Remember: Only one variable allowed on

the left side of the equals sign

But, that same variable can be on the right side

counter = 3;counter = counter + 5;cout << “counter = “ << counter;

What is the output???

Remember: The right side of the equals is ALWAYS evaluated first


power.cpp#include <iostream>using namespace std;

int main(){ double x, y; cout << "Enter x : "; cin >> x;

y = x; y = y * y; // Note: '=' is assignment, NOT equality. cout << "x^2 = " << y << endl;

y = y * x; // Note: '=' is assignment, NOT equality. cout << "x^3 = " << y << endl;

y = y * x; // Note: '=' is assignment, NOT equality. cout << "x^4 = " << y << endl;

return 0;}


> power.exe

Enter x : 1.5

x^2 = 2.25

x^3 = 3.375

x^4 = 5.0625

>


… y = x; y = y * y; // Note: '=' is assignment, NOT

equality. cout << "x^2 = " << y << endl;

y = y * x; // Note: '=' is assignment, NOT equality.

cout << "x^3 = " << y << endl;

y = y * x; // Note: '=' is assignment, NOT equality.

cout << "x^4 = " << y << endl;…

ERROR!#include <iostream>using namespace std;

int main(){ double x, y;

cout << "Enter x : "; cin >> x;

y = x^2; // SYNTAX ERROR. cout << "x^2 = " << y << endl;



return 0;}


> g++ powerError.cpp

powerError.cpp: In function ìnt main()':

powerError.cpp:13: invalid operands of types `double' and ìnt' to binary òperator^'



>


…13. y = x^2; // SYNTAX ERROR.14. cout << "x^2 = " << y << endl;15. 16. y = x^3; // SYNTAX ERROR.17. cout << "x^3 = " << y << endl;18. 19. y = x^4; // SYNTAX ERROR.20. cout << "x^4 = " << y << endl;…

ERROR!#include <iostream>using namespace std;

int main(){ double x, y;


x = y; cout << "x^2 = " << y * y << endl; cout << "x^3 = " << y * y * y << endl; cout << "x^4 = " << y * y * y * y << endl;

return 0;}


What is the error?

> power2Error.exe

Enter x : 2

x^2 = Inf

x^3 = -Inf

x^4 = Inf

>


… double x, y;


x = y; cout << "x^2 = " << y * y << endl; cout << "x^3 = " << y * y * y << endl; cout << "x^4 = " << y * y * y * y << endl;…

Useful shortcuts The statement: counter = counter + 5;

Can be shortened to counter += 5;

The following shortcuts work similarly (Memorize for the exam!):+=, -=, *=, /=, and %=

Example:product = product * ratio;product *= ratio;

Caveat (Why?):

product *= ratio + 1;

is the same as

product = product * (ratio + 1);

NOTproduct = product * ratio + 1;


Accumulation These types of statements are very useful!

total = total + 5; Start using them!

Trace through this code and track the value of the variable total

total = 0;total += 6; //total is now 6total += 3; //total is now 9total += 8; //total is now 17


Counting by 1 Counting by 1 is done a lot by programmers

We have a special shorthand operator (++) for incrementing a variable value by one

All of these are equivalent (which one would you use?):i = i + 1;i += 1;i++;

We also have a special decrement operator (--) for decrementing a variable value by one

i = i - 1;i -= 1;i--;

Programmer prefer using the increment/decrement operators


Initialization

Initialization is when a variable is assigned a value as it is declared or when assigned to its very first value

There is a shorthand for initializing a variable as it is declared!


initExample1.cpp


// initialization example

#include <iostream>#include <cmath>

using namespace std;

int main(){ double x(10.0); // initialize x to 10.0

cout << "The reciprocal of 10 is " << 1 / x << endl;

x = 15.0; cout << "The reciprocal of 15 is " << 1 / x << endl;

return 0; // exit program}

initExample2.cpp


// initialization example



int main(){ double x(3.0 + 4.0); // initialize x to 3 + 4 double y(5.0), z(6.0); // initialize y and z

cout << "The reciprocal of 3 + 4 is " << 1 / x << endl; cout << "The reciprocal of " << y << " is " << 1 / y << endl; cout << "The reciprocal of " << z << " is " << 1 / z << endl;


initExample3.cpp


// C style initialization example



int main(){ double x = 3.0 + 4.0; // C style initialization of x to 3 + 4 double y = 5.0, z = 6.0; // initialize y and z cout << "The reciprocal of 3+4 is " << 1 / x << endl; cout << "The reciprocal of " << y << " is " << 1 / y << endl; cout << "The reciprocal of " << z << " is " << 1 / z << endl;


Initialization

Rule of thumb: It is good programming practice to initialize all variables


noInit1.cpp


// example of missing initialization



int main(){ double x; double y(123.456);

cout << "x = " << x << endl; cout << "y = " << y << endl; cout << "e^(" << x << ") = " << exp(x) << endl; cout << "x + y = " << x + y << endl;


noInit1.cpp


… double x; double y(123.456);

cout << "x = " << x << endl; cout << "y = " << y << endl; cout << "e^(" << x << ") = " << exp(x) << endl; cout << "x + y = " << x + y << endl;…

> noInit1.exex = 0y = 123.456e^(0) = 1x+y = 123.456

>

noInit2.cpp


// example of missing initialization



int main(){ double y(123.456); double x;

cout << "x = " << x << endl; cout << "y = " << y << endl; cout << "e^(" << x << ") = " << exp(x) << endl; cout << "x + y = " << x + y << endl;


noInit2.cpp


… double y(123.456); double x;

cout << "x = " << x << endl; cout << "y = " << y << endl; cout << "e^(" << x << ") = " << exp(x) << endl; cout << "x + y = " << x + y << endl;…

> noInit2.exex = -7.69536e+304y = 123.456e^(-7.69536e+304) = 0x+y = -7.69536e+304

>

undeclaredVariable.cpp1. // Examples of an undeclared variable2. 3. #include <iostream>4. #include <cmath>5. using namespace std;6. 7. int main()8. {9. double y(0.0);10. y = 2.0 + x;11. 12. double x(0.0);13. x = 3.0 * 4.0;14. 15. cout << "x = " << x << endl;16. cout << "y = " << y << endl;17. 18. return 0;19. }


> g++ undeclaredVariable.cpp –o undeclaredVariable.exeundeclaredVariable.cpp: In function `int main()':undeclaredVariable.cpp:10: `x' undeclared (first use this function)undeclaredVariable.cpp:10: (Each undeclared identifier is reported only once for each function it appears in.)>


…7. int main()8. {9. double y(0.0);10. y = 2.0 + x;11. 12. double x(0.0);13. x = 3.0 * 4.0;14. 15. cout << "x = " << x << endl;16. cout << "y = " << y << endl;…

undefinedVariable.cpp// Examples of an undefined variable

#include <iostream>#include <cmath>using namespace std;

int main(){ double y; double x;

y = 2.0 + x; x = 3.0 * 4.0;

cout << "x = " << x << endl; cout << "y = " << y << endl;

return 0;}


Try running this program!

Warning

Remember: Make sure you have already assigned values to variables BEFORE they are used in these computations!


Coercion Assigning an integer to a floating point variable

converts the integer to a floating point number

Example:

double y = 3;

Assigning a floating point number to an integer truncates the number and converts it to an integer

Example:

int x = 3.4;


coercion.cpp1. // assigning float to integer or integer to float2. 3. #include <iostream>4. using namespace std;5. 6. int main()7. {8. int x(0);9. double y(0.0);10. 11. x = 3.4; // assign floating point number to int12. y = 3; // assign integer to a floating point variable13. 14. cout << "x = " << x << endl; // x equals 315. cout << "y = " << y << endl; // 3 is output, but y is still a float16. 17. cout << "1/x = " << 1/x << endl; // 0 since x is an integer18. cout << "1/y = " << 1/y << endl; // 0.333333 since y is a

float19.

20. return 0;21. }


> g++ coercion.cpp –o coercion.execoercion.cpp: In function ìnt main()':coercion.cpp:11: warning: assignment to ìnt' from `double'coercion.cpp:11: warning: argument to ìnt' from `double'>


…8. int x(0);9. double y(0.0);10. 11. x = 3.4; // assign floating point number to int12. y = 3; // assign integer to a floating point variable13. 14. cout << "x = " << x << endl; // x equals 3.15. cout << "y = " << y << endl; // 3 is output.. but y is still a

float16. 17. cout << "1/x = " << 1/x << endl; // 0 since x is an integer18. cout << "1/y = " << 1/y << endl; // 0.333333 since y is a float…

> coercion.exex = 3y = 31/x = 01/y = 0.333333>


…8. int x(0);9. double y(0.0);10. 11. x = 3.4; // assign floating point number to int12. y = 3; // assign integer to a floating point variable13. 14. cout << "x = " << x << endl; // x equals 3.15. cout << "y = " << y << endl; // 3 is output.. but y is still a float16. 17. cout << "1 / x = " << 1 / x << endl; // 0 since x is an integer18. cout << "1 / y = " << 1 / y << endl; // 0.333333 since y is a float…

Coercion Remember the data type character?

A character is represented as an integer with size of a single byte

Assigning an integer to a char variable converts the integer to a character

Example:

char c = 88; // c is now ‘X’// See your ASCII

table


coercion2.cpp#include <iostream>using namespace std;int main(){ int x1(71), x2(111), x3(32), x4(66), x5(117), x6(99), x7(107), x8(115),

x9(33); char c1, c2, c3, c4, c5, c6, c7, c8, c9;

c1 = x1; c2 = x2; c3 = x3; c4 = x4; c5 = x5; c6 = x6; c7 = x7; c8 = x8; c9 = x9;

cout << c1 << c2 << c3 << c4 << c5 << c6 << c7 << c8 << c9 << endl;

return 0;}


What is the output?

cse1222: lecture 3the ohio state university1. assignment operations the c++ assignment operator is:...

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