OOP 2012 - Hint: Dynamic allocation in c++

Transcript

1. Dynamic Allocation in C++ allan914.120418 (update: 120420)
2. Example 1 #include<iostream> using namespace std; int main() { int* a; int n; cin >> n; a=new int [n]; for(int i=0;i<n;i++) a[i]=i+1; for(int i=0;i<n;i++) cout << a[i] << " "; delete [] a; return 0; }
3. Example 1: Result  Sample Input 10  Sample Output 1 2 3 4 5 6 7 8 9 10
4. Example 2 #include<iostream> using namespace std; int main() { int** a; int n,m; cin >> n; cin >> m; a=new int* [n]; for(int i=0;i<n;i++) a[i]=new int [m]; for(int i=0;i<n;i++) for(int j=0;j<m;j++) a[i][j]=i+j+1; for(int i=0;i<n;i++) { for(int j=0;j<m;j++) cout << a[i][j] << " "; cout << endl; } for(int i=0;i<n;i++) delete [] a[i]; delete [] a; return 0; }
5. Example 2: Result  Sample Input 5 4  Sample Output 1 2 3 4 2 3 4 5 3 4 5 6 4 5 6 7 5 6 7 8
6. Example 3 #include<iostream> using namespace std; int main() { int* a; int n,m; cin >> n; cin >> m; a=new int [n*m]; int** b; b=new int* [n]; for(int i=0;i<n;i++) b[i]=&(a[n*i]); for(int i=0;i<n;i++) for(int j=0;j<m;j++) b[i][j]=i+j+1; for(int i=0;i<n;i++) { for(int j=0;j<m;j++) cout << b[i][j] << " "; //cautious with CodeBlocks ! cout << endl; } delete [] b; delete [] a; return 0; }
7. Example 3: Result  Sample Input 5 4  Sample Output 1 2 3 4 2 3 4 5 3 4 5 6 4 5 6 7 5 6 7 8
8. Example 4 // Headers emitted, cautious with CodeBlocks ! void* new2d(int n,int m,int size) { void **a = new void* [m*sizeof(void*) + n*m*size]; for(int j=0;j<m;j++) a[j] = ((char *)(a+m)) + j*n*size; return a; } int main() { int** a; int n,m; cin >> n; cin >> m; a = (int**)new2d(m,n,sizeof(int)); for(int i=0;i<n;i++) for(int j=0;j<m;j++) a[i][j]=i+j+1; for(int i=0;i<n;i++) { for(int j=0;j<m;j++) cout << a[i][j] << " "; cout << endl; } delete [] a; return 0; }
9. Example 4: Result  Sample Input 5 4  Sample Output 1 2 3 4 2 3 4 5 3 4 5 6 4 5 6 7 5 6 7 8
10. Example 5 #include<iostream> #include<vector> using namespace std; int main() { int n,m; cin >> n; cin >> m; vector<vector<int> > a(n, vector<int>(m)); for(int i=0;i<n;i++) for(int j=0;j<m;j++) a[i][j]=i+j+1; for(int i=0;i<n;i++) { for(int j=0;j<m;j++) cout << a[i][j] << " "; cout << endl; } return 0; }
11. Example 5: Result  Sample Input 5 4  Sample Output 1 2 3 4 2 3 4 5 3 4 5 6 4 5 6 7 5 6 7 8