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計算機概論實習 2007-03-16

計算機概論實習 2007-03-16. Integral Stream Base expression: dec, oct, hex, setbase, and showbase. Use header <iomanip> Integers normally base 10 (decimal) Stream manipulators to change base dec (resets to base 10) cout << dec << 1000  1000 hex (base 16) cout << hex << 1000;  3e8

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計算機概論實習 2007-03-16

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  1. 計算機概論實習2007-03-16

  2. Integral Stream Base expression: dec, oct, hex, setbase, and showbase • Use header <iomanip> • Integers normally base 10 (decimal) • Stream manipulators to change base • dec (resets to base 10) cout << dec << 1000  1000 • hex (base 16) cout << hex << 1000;  3e8 • oct (base 8) cout << oct << 1000;  1750

  3. Integral Stream Base expression: dec, oct, hex, setbase, and showbase • setbase(newBase) • One of 8, 10, or 16 cout << setbase(dec) << 1000; • Base remains same until explicitly changed • showbase • Forces base of number to be shown • Decimal numbers default 1000 • Preceding 0x or 0X for hex 0x3e8 • Preceding 0 for octal 01750 • Remove with noshowbase

  4. Floating-Point Precision (precision, setprecision) • Set precision of floating point numbers • Number of digits to right of decimal • setprecision stream manipulator • Pass number of decimal points • cout << setprecision(5) • precision member function • cout.precision(newPrecision) • With no arguments, returns current precision • Settings remain until changed explicitly

  5. precision example int main(){ double root2 = sqrt( 2.0 ); //sqrt(2.0) = 1.414213562….. for (int i = 0; i <= 11 ; i++){ cout.precision( i ); cout << root2 << endl; } return 0; } 1.41421 1 1.4 1.41 1.414 1.4142 1.41421 1.414214 1.4142136 1.41421356 1.414213562 1.4142135624

  6. Field Width (width, setw) • width member function (base class ios_base) • Sets field width • Number of character positions for output • Can also use setw stream manipulator

  7. width, setw example int main(){ constint SIZE= 80; char buffer[SIZE]; cout << "Enter a sentence:" << endl; cin.get(buffer, SIZE); cout << "set width 5" << endl; cout.width(5); cout << buffer << endl; cout << "set width 6\n" << setw(6) << buffer << endl; return 0; }

  8. Trailing Zeros and Decimal Points (showpoint) • showpoint • Forces decimal number to print with trailing zeros • For decimal number 79.0 • 79 without showpoint • 79.000000 with showpoint (up to level of precision) • Reset with noshowpoint

  9. showpoint example int main(){ cout << showpoint << "After using showpoint" << endl << "9.9900 prints as: " << 9.9900 << endl << "9.9000 prints as: " << 9.9000 << endl << "9.0000 prints as: " << 9.0000 << endl << "9 prints as: " << 9 << endl; return 0; } After using showpoint 9.9900 prints as: 9.99000 9.9000 prints as: 9.90000 9.0000 prints as: 9.00000 9 prints as: 9

  10. Justification (left, right and internal) • left stream manipulator • Left-justified, padding to right • right stream manipulator • Right-justified, padding to left • internal • Number's sign left-justified • Number's value right-justified + 123 • showpos forces sign to print • Remove with noshowpos

  11. left, right and internal example int x = 12345; cout << showpos; cout << "Default is right justified:" << endl << setw( 10 ) << x; cout << "\n\nUse std::left to left justify x:\n" << left << setw( 10 ) << x; cout << "\n\nUse std::right to right justify x:\n" << right << setw( 10 ) << x << endl; cout << "\n\nUse std::internal to internal justify x:\n" << internal << setw(10) << x << endl;

  12. left, right and internal example Default is right justified: +12345 Use std::left to left justify x: +12345 Use std::right to right justify x: +12345 Use std::internal to internal justify x: + 12345

  13. Padding (fill, setfill) • Set fill character used in padding • fill member function • cout.fill('*') cout.fill( '*' ); cout << setw( 10 ) << dec << x << endl; *****10000 • setfill stream manipulator • setfill( '*' ) cout << setfill( '*' ) << setw( 10 ) << dec << x << endl;

  14. Floating-Point Numbers; scientific and fixed) • Stream manipulator scientific • Forces scientific notation • 1.946000e+009 • Stream manipulator fixed • Forces fixed point format • Prints number of decimals specified by precision • 1946000000.000000

  15. Scientific and fixed example double x = 0.001234567; double y = 1.946e9; cout << "Displayed in default format:" << endl << x << '\t' << y << endl; cout << "\nDisplayed in scientific format:" << endl << scientific << x << '\t' << y << endl; cout << "\nDisplayed in fixed format:" << endl << fixed << x << '\t' << y << endl;

  16. Uppercase/Lowercase Control (uppercase) • Stream manipulator uppercase • Uppercase E in scientific notation • 1E10 • Uppercase X in hex notation and uppercase hex letters • 0XABCD • By default, lowercase • Reset with nouppercase

  17. Specifying Boolean Format (boolalpha) • Data type bool • Values true or false • Outputs 0 (false) or 1 (true) when used with << • Displayed as integers • Stream manipulator boolalpha • Display strings "true" and "false" • Reset with noboolalpha bool boolvalue = true; cout << “The result is " << boolalpha << boolvalue;  The result is true

  18. Setting and Resetting the Format State via Member-Function flags • Can save/restore format states • After apply many changes, may want to restore original • Member function flags • cout.flags() • With no argument • Returns current state as fmtflags object • Namespace ios_base • Represents format state • cout.flags(0) : reset format • With fmtflags argument • Sets state • Returns previous state

  19. Example int main(){ int integerValue = 1000; double doubleValue = 0.0947628; cout << "The value of the flags variable is: " << cout.flags() << "\nPrint int and double in original format:\n" << integerValue << '\t' << doubleValue << endl << endl; ios_base::fmtflags originalFormat = cout.flags(); cout << showbase << oct << scientific; // change format

  20. Example cout << "The value of the flags variable is: " << cout.flags() << "\nPrint int and double in a new format:\n" << integerValue << '\t' << doubleValue << endl << endl; cout.flags( originalFormat ); // restore format cout << "The restored value of the flags variable is: " << cout.flags() << "\nPrint values in original format again:\n" << integerValue << '\t' << doubleValue << endl; return 0; }

  21. The value of the flags variable is: 513 Print int and double in original format: 1000 0.0947628   The value of the flags variable is: 012011 Print int and double in a new format: 01750 9.476280e-002 The restored value of the flags variable is: 513 Print values in original format again: 1000 0.0947628

  22. Practice 2 (P2) • Please write a program which input interface is as follows: • and the output interface is like below: 請輸入學生的三個成績 >: 80,90,90 10字元寛 10字元寛 10字元寛 國文 英文 數學 平均 80 90 90 86.67

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