Basics

Basics • A First Program • Variables, Objects, and Types • C++ Built-In Types and Operations • Input and Output • Operator Precedence and Associativity • if Statements • Loops • Declarations • Arrays

... • Pointers • Pointers and Arrays • const Pointers and Pointers to const Objects • Runtime Array Size • Character Strings • References • Functions

Statements, Functions, {}, ;, Comments, ... • void f() { • int a = 1, b = 2, c = 3; • a = b + c; // This part is a comment. • /* This is a comment. */ • } C Programmers: Prefer C++ style comments: //... instead of /* ... */ if (a > b) { /* int t = a; /* swap a and b */ a = b; b = t; */ } if (a > b) { // int t = a; // swap a and b // a = b; // b = t; }

The most trivial C++ programm • int main() { • return 0; • } Every C++ program must contain exactly one function named main. It should return an integer value.

First program with I/O • #include <iostream> • int main() { • // Read and print three floating point numbers • double a, b, c; • std::cin >> a >> b >> c; • std::cout << a << ", " << b << ", " << c << std::endl; • return 0; • } Include iostream in any file that contains C++ input or output operations. C Programmers: Use iostream instead of stdio.h.

First program with I/O: new/old C++ • #include <iostream> • int main() { • // ... • std::cin >> a >> b >> c; • std::cout << a << ", " << b << ", " << c << std::endl; • // ... • } • #include <iostream> • using namespace std; • int main() { • //... • cin >> a >> b >> c; • #include <iostream> • using std::cin; • using std::cout; • using std::endl; • int main() { • //... • cin >> a >> b >> c; • #include <iostream.h> • int main() { • //... • cin >> a >> b >> c;

x- and y-intercepts of ax + by + c = 0 • #include <iostream.h> • int main() { • // Read the coefficients of a line equation in the form • // ax+by+c = 0 • // then print the line's x- and y-intercepts. • // Read the equation coefficients. • float a, b, c; • cin >> a >> b >> c; • // Print the equation coefficients. • cout << "Coefficients: " << a << ", " << b << ", " << c << endl;

// Compute and print the x-intercept. • cout << "x-intercept: "; • if (a != 0) { • cout << -c / a << ", "; • } • else { • cout << "none, "; • } • // Compute and print the y-intercept. • cout << "y-intercept: "; • if (b != 0) { • cout << -c / b << endl; • } • else { • cout << "none" << endl; • } • return 0; • }

Microscopic Viewpoint to a Program A program specifies a procedure for altering the values of objects, using symbolic references to the objects called variables. • An object is an area of the computer´s memory that has a value (a particular bit pattern) stored in it. • The type of an object specifies how the bits are stored as the object´s value are to be manipulated. • A variable is an association between a name and an object; the type of a variable specifies the type of objects that the variable can be associated with.

int 3 float 12.1 float 12.1 int 5 float 10.0 int i float x float x int i : : : : float x float a float r int j : : : : float or int Variables, References, Unions • int i = 3; • float x = 10.0; • i = 5; • x = 12.1; • float& a = x; • union { • float r; • int j; • } Avoid union types.

Numeric Types and Typical Sizes • C++ Type Size (bytes) • char 1 • short int 2 signed • int 2 or 4 unsigned • long int 4 or 8 • float 4 • double 8 • long double 16 • 1 = sizeof(char)  sizeof(short)  sizeof(int)  sizeof(long) • sizeof(float)  sizeof(double)  sizeof (long double) • Check the header files: <limits.h> <float.h> <limits> .. Do not use unsigned integers. Use int and double.

Constants • 1234 decimal integer • 0643 octal integer • 0x37cd hex integer • 8.4e-2, 93.2 double floating-point • Suffixes for Constants • no suffix, decimal int, long int, unsigned long int • no suffix, octal or hex int, unsigned int, long int, unsigned long int • l or L long int, unsigned long int • u or U unsigned int, unsigned long int • ul or UL unsigned long int • no suffix, floating-point double • f or F float • l or L long double

x ++ Postincrement ++ x Preincrement x -- Postdecrement -- x Predecrement + x Unary plus - x Unary minus x * y Multiply x / y Divide x % y Modulus x + y Add x - y Subtract int i = 1; cout << i << ", "; cout << (++i) << ", "; cout << i << ", "; cout << (i++) << ", "; cout << i << endl; Arithmetic Operators

Logical Values and Operators • 0 False value • nonzero True value • !x Logical negation • x && y Logical and • x || y Logical inclusive or Characters cout << ('a'<'b') << " " << ('1'>='3') << " " << ('a'!='A') << " " << ('a'=='a') << ('z'>'y') << endl; • \n Newline \r Carriage return \? Question mark • \t Horizontal tab \f Form feed \' Single quote • \v Vertical tab \a Alert \" Double qoute • \b Backspace \\ Backslash \ddd Octal code

Enumerations • An enumeration is an ordered set of names: • enum Color {red, orange, yellow, green, blue, indigo, violet); • Color c = green; • enum Polygon {triangle = 3; quadrilateral = 4; pentagon = 5}; Assignment Operators • = • += -= *= /= %= >>= <<= &= ^= |= • a op= expression; is equivalent to a = a op (expression) • a += b; is equivalent to a = a + b;

streams: cin cout cerr << >> • cin >> x; • cin >> x >> y; • cout << x; • cout << endl; • int i = 1; int i = 1; • int j = 2; int j =2; • cout << i << j; cout << i << " " << j; • cout << endl; cout << endl; • int i = 1;Insert your own whitespace on output. • int j = 2; • cout << i << endl << j << endl;

Fortran compatible I/O • #include <iostream.h> • #include <iomanip.h> • double a = 3.14159; • double b = 1 / a; • double c = 10 * a; • // Use FORTRAN compatibility output. • cout << setiosflags(ios::showpoint | ios::uppercase); • // Write data in G15.8 format. • cout << setw(15) << setprecision(8) << a; • cout << setw(15) << setprecision(8) << b; • // Write in F10.3 format • cout << setiosflags(ios::fixed); • cout << setw(10) << setprecision(3) << c << endl;

File I/O • #include <iostream.h> • #include <fstream.h> • //... • ofstream out("pi.out"); • out << 3.14159 << endl; • ofstreamoutput file stream • ifstreaminput file stream

Quick Reference: Expressions 1 • Each box holds operators with the same precedence. • Operators in higher boxes have higher precedence. • Unary and assignment operators are right-associative. • All others are left associative.

Quick Reference: Expressions 2

Quick Reference: Expressions 6 Use parentheses and spacing to make expressions easier to read.

if Statements • if (current_temp > maximum_safe_temp) { • cerr << "EMERGENCY: Too hot--flushing" << endl; flushWithWater(); • } • if (current_temp > maximum_safe_temp) • cerr << "EMERGENCY: Too hot--flushing" << endl; • // WRONG! • if (current_temp > maximum_safe_temp) • cerr << "EMERGENCY: Too hot--flushing" << endl; • flushWithWater(); Select a code formatting style and use it consistently. Use a block for an if statement body.

if (current_temp > maximum_safe_temp) { • // Emergency cool down. • cerr << "EMERGENCY: Too hot--flushing" << endl; • flushWithWater(); • } else { • // Normal control strategy. • if (current_temp > operating_temp + temp_tolerance) { • heaterOff(); • if (current_temp > operating_temp + 2*temp_tolerance) { • coolingWaterOn(); • } • } • if (current_temp < operating_temp - temp_tolerance) { • coolingWaterOff(); • if (current_temp < operating_temp - 2*temp_tolerance) { • heaterOn(); • } • } • }

if ?: • if (expression) { • block-contents; • } • if (expression) { • block-1-contents; • } else { • block-2-contents; • } • expression ? true-value : false-value; • x = (x<0) ? -x : x; // x = abs(x) Use the conditional operator only for simple tests that fit on one line.

switch In switch statements each choice must have a closing break, or be on the same line as another choice or there should be a comment to indicate that the fall-through is the desired action. • switch(cin.get()){ • case 'X': exit(0); • case 'H': • help(); • break; • case 'A': • case 'B': • // do something • break; • default: • cout << "try again" << endl; • }

Loops: while, do-while • float x; • while (cin >> x) { • cout << setw(25) << x << setw(25) << sqrt(x) << endl; • } • ch2/Newton.C • x = initial_guess; • do { • dx = f(x) / fprime(x); • x -= dx; • } while (abs(dx) > desired_accuracy); Use a while loop when it is possible that the loop body should not be executed. Use a do loop when the body should always be executed at least once.

Loops: for • for(init-statement; continue-expression; increment-expression) { • ... // loop body • } • for(int i = 1; i <= 10; i++) { • cout<< "i= " << i << endl; • }

break , continue,goto • break: terminate innermost enclosing while, do, for, or switch • continue: go to bottom of loop in while, do or for • ch2/break.C • int x; • while(cin >> x) { • if(x < 0) { • cout << "Negative number " << x << " read" << endl; • break; • } • // regular input processing • } Use break and continue sparingly and only when their meaning will be clear. Do not use goto.

Quick Reference:Control Statements • break; leave current block or case • continue; continue with next iteration • goto label; jump to label • label: statement set label • while(expr)statement repeat stmt as long as expr is true • do statement while(expr) repeat stmt until expr is false • expr1; • while(expr2){ • for(expr1;expr2;expr3) statement statement • expr3; • } • if(expr)statement • if(expr)statement else statement • switch (expr) { expr is evaluated and compared to • case const_expr: statement the case const_expr; execution • case const_expr: statement continues at the first match; • ... caution: must use break to leave the • default: statement switch • }

Declarations • Declaration Attributes Declarator Initializer • int x; int x • int x = 3; int x = 3 • float y = 1.1; float y = 1.1 • int a[3]; int a[3] • const float e=2.7 const,float e = 2.7 Use one declaration statement for each variable; declare each variable just before its first use and initialize it at the same time.

const, typedef • const float h = 6.6256e-34; // Planck's constant (mks units) • void f() { • float x; • cin >> x; // Read value of x • const float xc = x; • ... • } • ch2/typedef.C • typedef float distance; • typedef float force; • distance d = 10; • force f; • f = d; Use typedefs for C++ built-in types to ensure portable numerical results and persistence schemes.

Arrays • float x[100]; // x[0] ... x[99] • float x[3] = {1.1, 2.2, 3.3}; • float x[] = {1.1, 2.2, 3.3}; • float m[3][3], m1[3][3], m2[3][3]; • // Code that initializes m1 and m2 ... • // m = m1 * m2 • for (int i = 0; i < 3; i++) { • for (int j = 0; j < 3; j++) { • double sum = 0.0; • for (int k = 0; k < 3; k++) { • sum += m1[i][k] * m2[k][j]; • } • m[i][j] = sum; • } • }

C++ arrays use 0-origin subscripting and the elements are stored row-wise. • Warning: m[1,2] is a valid C++ expression, but it does not access a multidimensional array. • Multidimensional arrays are arrays of arrays. • int m[2][3] = { • {1,2,3}, • {4,5,6} • }; • m consists of two elements (rows), each a one-dimensional array of three elements.

int* p int* p : : int j int i int i : : : int 3 int 3 int* int 4 int* Pointers • int* p; • int i = 3; • p = &i; • int j = 4; • P = &j; • *p = 5; • p = 0; • ... • if (p != 0) cout << "Pointer " << p << " points to " << *p << endl; &x address of x *p indirection, value of object pointed to by p

float[5] x : x[0]: x[1]: x[2]: x[3]: x[4]: float float float float float Conversion float* Pointers and Arrays • float x[5]; Whenever x is used in an expression - except as the operand of &, sizeof or to initialize a reference - it is converted into a pointer to the first element of the array. x is of type array of float, but used as pointer to float.

float[5] x : x[0]: x[1]: x[2]: x[3]: x[4]: float float float float float Conversion float* Arithmetic on Pointers • x + 2 • x points to x[0] • x+i points to x[i] • *(x+i)is equivalent to x[i] • x+i is equivalent to &x[i] • Integers can be added (or subtracted) to a pointer to an array element. • It acts as offset. The result is a pointer of the same type, which points to the element the specified number of elements away.

float x[10]; • // ... initialize x ... • float* left = &x[0]; • float* right = &x[9]; • while (left < right) { • float temp = *left; • *left++ = *right; • *right-- = temp; • } • float x[10]; • float* p = &x[10]; • while (p != x) *--p = 0.0;

const Pointers, Pointers to const Objects • const float pi = 3.14159; • const float* p = π • pi = 2; // Compile Error • *p = 2; // Compile Error • float a, b; • float* const p1 = &a; • *p1 = 10; • p1 = &b; // Compile Error • const float e = 2.718281828; • const float* const p2 = &e; Read complex declarations from the identifier back toward the beginning of the statement. C Programmers: Do not use #define to define symbolic constants, use const for individual constants or enum for enumerations.

// Create arrays with the // desired number of elements int n; cin >> n; float* const x = new float[n]; float* const y = new float[n]; // Read the data points for (int i = 0; i < n; i++) { cin >> x[i] >> y[i]; } // Accumulate sums Sx and Sy // in double precision double sx = 0.0; double sy = 0.0; for (i = 0; i < n; i++) { sx += x[i]; sy += y[i]; } // Compute coefficients double sx_over_n = sx / n; double stt = 0.0; double b = 0.0; for (i = 0; i < n; i++) { double ti = x[i] - sx_over_n; stt += ti * ti; b += ti * y[i]; } b /= stt; double a = (sy - sx * b) / n; delete [] x; delete [] y; cout << a << " " << b << endl; Runtime Array Size

Pointer Operators • *p Indirection • &x Pointer to object • a[i] Array subscript • p->m Class member selection • ++p, p++ Pre(Post)increment to next element • --p, p-- Pre(Post)decrement to previous element • p+=n Increment by n elements • p-=n Decrement by n elements • p+n Offset by n elements • p-n Negative offset by n elements • new T Allocate object • new T[n] Allocate array of n objects • delete p Delete object • delete []p Delete array of objects

H H e a n I i \0 i c w s \0 ? t ? a ? N ? o Character Strings • C character strings are a special case of arrays and array initialization: • char hello1[] = {'H','i'}; • char hello2[] = "Hi"; • char name[15] = "Isaac Newton"; Use the C++ standard library (or STL) string class rather then const char* where possible.

Functions, void doNothing(){} • doublecoulombsLaw(double q1, double q2, double r) { • // Coulomb's law for the force acting on two point charges • // q1 and q2 at a distance r. MKS units are used. • const double k = 8.9875e9; // nt-m**2/coul**2 • return k * q1 * q2 / (r * r); • } • int main() { • cout << coulombsLaw(1.6e-19, 1.6e-19, 5.3e-11) << " newtons\n"; • return 0; • } • return-value-typefunction-name(argument-list) { • function-body • }

Function Prototypes and Header Files • extern double coulombsLaw(double q1, double q2, double r); • #include <iostream.h> • #include "coulombsLaw.h" • int main() { • cout << coulombsLaw(1.6e-19, 1.6e-19, 5.3e-11) << ... • return 0; • } • #include "coulombsLaw.h" • double coulombsLaw(double q1, double q2, double r) { • ... • return k * q1 * q2 / (r * r); • }

Basics

Basics

Presentation Transcript

Basics

Basics

Basics

Basics

Basics

BASICS

Basics

Basics

Basics

Basics

Basics

Basics

Basics

Basics

Basics

Basics

Basics

Basics

basics