CSE202: Lecture 3The Ohio State University1 Assignment

CSE202: Lecture 3 The Ohio State University 1

Assignment


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

• A variable, and only one variable, must be on the left. Any 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);

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

• 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;


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^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;…

Assignment Variations



Useful shortcuts• counter = counter + 5; can be shortened to counter += 5;• The following shortcuts work in the same way:

+=, -=, *=, /=, and %=

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

• Caveat:product *= ratio + 1;

is the same asproduct = product * (ratio + 1);

NOTproduct = product * ratio + 1;


Accumulation

• Assignments like total = total + 5; are quite useful in programming. For instance:

total = 0;

total += 6; //total is now 6




Counting by 1

• Counting by 1 is so common and useful that there is a special operator for it called the increment operator (++).

• All of these are equivalent:

i = i + 1; or i += 1; or i++;

• Similarly, the decrement operator (--) can be used to decrease a variable by 1.

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

Variable Initialization



Initialization

• Variables can be assigned a value as they are declared. This is called initializing.


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

• 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 ìnt 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

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

Coercion



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 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 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

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

• Example:

char c = 88;

// c is now ‘X’


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?

Documents

CSE202: Lecture 3The Ohio State University1 Assignment