Midterm Exam (1) 成績分佈

1. Midterm Exam (1) 成績分佈

2. 答題統計

3. Chapter 7Arrays and Vectors

4. Declaring an Array with an Initializer List • constintarraySize = 10; • Prevent using “magic numbers”, because the program may include other 10s that is not array size. • int s[arraySize] = { 32, 27, 64 }; • The remaining elements are initialized to zero. • int s[10] = { }; // initialize all elements to 0 • int a[] = {1, 2, 3, 4, 5}; • The compiler will create a five-element array.

5. Fig. 7.9 Bar Chart Printing (P.308) constintarraySize = 11; int n[ arraySize ] = { 0, 0, 0, 0, 0, 0, 1, 2, 4, 2, 1 }; for ( inti = 0; i < arraySize; ++i ) { cout << i * 10 << "-" << ( i * 10 ) + 9 << ": "; // print bar of asterisks for ( int stars = 0; stars < n[ i ]; ++stars ) cout << '*'; cout << endl; // start a new line of output } // end outer for Grade distribution: 0-9: 10-19: 20-29: 30-39: 40-49: 50-59: 60-69: * 70-79: ** 80-89: **** 90-99: ** 100: * pronounced “n sub i”

6. Fig. 7.10 Dice Rolling (P.310) constintarraySize = 7; // ignore element zero int frequency[ arraySize ] = {}; // initialize elements to 0 srand( time( 0 ) ); // seed random number generator // roll die 6,000,000 times; use die value as frequency index for ( int roll = 1; roll <= 6000000; ++roll ) ++frequency[ 1 + rand() % 6 ]; // array elements as counters cout << "Face" << setw( 13 ) << "Frequency" << endl; // output each array element's value for ( int face = 1; face < arraySize; ++face ) cout << setw( 4 ) << face << setw( 13 ) << frequency[ face ] << endl; Compare fig06_09.cpp on P.240

7. Common Programming Error 7.5 (P.312) • Referring to an element outside the array bounds is an execution-time logic error. It isn’t a syntax error. • Which implies that the compiler will not check this for you. int c[4] = {9, 10, 11, 12}; int b[4] = {5, 6, 7, 8}; int a[4] = {1, 2, 3, 4}; b[-1] = 99; b[4] = 44; cout << a[3] << '\t' << c[0] << endl; cout << &a[3] << '\t' << &b[-1] << endl; cout << &c[0] << '\t' << &b[4] << endl; b[-1] b[4]

8. Fig. 7.13 Passing Arrays to a Function (P.316) void modifyArray( int [], int ); void modifyArray( int b[], intsizeOfArray ) { // multiply each array element by 2 for ( int k = 0; k < sizeOfArray; ++k ) b[ k ] *= 2; } // end function modifyArray Even if you include the array size, it will be ignored by the compiler.

9. Fig. 7.14 const parameter (P.318) void tryToModifyArray( constint b[] ) { b[ 0 ] /= 2; } compilation error if you modify elements in this array

10. Fig. 7.15 Class Variable (P.319) class GradeBook { public: // constant -- number of students who took the test static constint students = 10; Keyword static in this variable declaration indicates that the data member is shared by all objects of the class. Actually, you can even access this “class variable” by GradeBook::student before any object is created. (P.324)

11. Fig. 7.21 Multidimensional Arrays (P.330) • void printArray( constint[][ 3 ] ); • The size of the first dimension is not required. • All subsequent dimension sizes are required. • constint rows = 2; • constint columns = 3; • int array1[ rows ][ columns ] = { { 1, 2, 3 }, { 4, 5, 6 } }; • You may omit the inner braces. Then it is equivalent to { 1, 2, 3, 4, 5, 6 }. • int array2[ rows ][ columns ] = { 1, 2, 3, 4, 5 }; • This is equivalent to { {1, 2, 3}, {4, 5, 0} }. • int array3[ rows ][ columns ] = { { 1, 2 }, { 4 } }; • This is equivalent to { {1, 2, 0}, {4, 0, 0} }.

12. Fig 7.25 vector (P.340) copy all elements in a vector to another vector #include <iostream> #include <vector> using std::vector; using std::cout; using std::endl; int main() { vector<int> a(7); vector<int> b(7); inti; for (i=0; i<a.size(); ++i) a.at(i) = i; b = a; for (i=0; i<b.size(); ++i) cout << b.at(i); cout << endl; return 0; } a 7-element array a vector knows its own size similar to a[i] = i;

13. Fig 7.25 try-catch (P.341) #include <iostream> #include <vector> #include <stdexcept> using std::out_of_range; using std::vector; using std::cout; using std::endl; int main() { vector<int> a(7); // automatically initialed to 0. try { cout << a.at(15) << endl; } catch (out_of_range &ex) { cout << "An exception occurred: " << ex.what() << endl; } cout << "Program ends normally." << endl; return 0; }