Reverse 2D arrays

for (int i = 0; i < array_length/2; ++i) {     int end = array_length - 1;   for (int j = 0; j < 5; ++j)   {      //do a xor swap on the two values:      //array[j] and array[end][j]   }   --end;}

boost::array<boost::array<int, 5>, 4> my_array;std::reverse(my_array.begin(), my_array.end());

// TODO... I will edit this from home

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Original post by Alpha_ProgDes for (int i = 0; i < array_length/2; ++i) { int end = array_length - 1; for (int j = 0; j < 5; ++j) { //do a xor swap on the two values: //array[j] and array[end][j] } --end;}

std::vector<std::vector<int> > a_vector;populate a_vector;std::vector<std::vector<int> > reversed_vector(a_vector.rbegin(), a_vector.rend());

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Original post by Deyja std::vector<std::vector<int> > a_vector;populate a_vector;std::vector<std::vector<int> > reversed_vector(a_vector.rbegin(), a_vector.rend());

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are you sure that not only reverses the rows but also the order of the numbers?

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Original post by OpenGL_Guru Quote: Original post by Deyja std::vector<std::vector<int> > a_vector;populate a_vector;std::vector<std::vector<int> > reversed_vector(a_vector.rbegin(), a_vector.rend()); assume i dont have std. thats what i am assuming :)

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assume i dont have std. thats what i am assuming :)

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Original post by Alpha_ProgDes int end = array_length - 1;for (int i = 0; i < array_length/2; ++i) { //int end = array_length - 1; // end will never change with this line here for (int j = 0; j < 5; ++j) { //do a xor swap on the two values: //array[j] and array[end][j] } --end;}

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Original post by Rasmadrak stupid question, but... can't you just read it from the back? or do you need this array to be used in both directions "simultaniously"?

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Original post by nicksterdomus Quote: Original post by Alpha_ProgDes int end = array_length - 1;for (int i = 0; i < array_length/2; ++i) { //int end = array_length - 1; // end will never change with this line here for (int j = 0; j < 5; ++j) { //do a xor swap on the two values: //array[j] and array[end][j] } --end;} Now it should work.

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Original post by OpenGL_Guru [yes but itseems still you are swapping fromthe wrong end of the end of the array. if the array length is 20 then you would swap array[0][0] and array [19][0] which is not right. what the first row should be would be to swap [0][0],[15][0] & [0][1],[16][1] & [0][2],[17][2] etc etc

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Original post by Conner McCloud Quote: Original post by OpenGL_Guru [yes but itseems still you are swapping fromthe wrong end of the end of the array. if the array length is 20 then you would swap array[0][0] and array [19][0] which is not right. what the first row should be would be to swap [0][0],[15][0] & [0][1],[16][1] & [0][2],[17][2] etc etc You aren't making any sense. If the array length is 20, then why would you swap row 0 with row 15? That isn't a reversal, that's just a shuffling. CM

for r = 0; r < rows/2; r++	for c = 0; c < cols; c++		swap( array[r][c], array[rows - r - 1][c] )

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Original post by OpenGL_Guru sure its a reversal.. its a reverals of the ROWS with their columns..not the data itself..

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Original post by Conner McCloud Quote: Original post by OpenGL_Guru sure its a reversal.. its a reverals of the ROWS with their columns..not the data itself.. Show an example of what you mean. And no, your first one does not count. You've been given code that implements it, and rejected it. CM

int end = array_length - 1;for (int i = 0; i < array_length/2; ++i) {     //int end = array_length - 1;     // end will never change with this line here   for (int j = 0; j < 5; ++j)   {      //do a xor swap on the two values:      //array[j] and array[end][j]   }   --end;}

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Original post by Anonymous Poster Quote: Original post by OpenGL_Guru Quote: Original post by Conner McCloud Quote: Original post by OpenGL_Guru sure its a reversal.. its a reverals of the ROWS with their columns..not the data itself.. Show an example of what you mean. And no, your first one does not count. You've been given code that implements it, and rejected it. CM which code are you talking about.. *** Source Snippet Removed *** lets me give you the 2D array again: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 therefore array_length = 20 end = 19 so the first time this code wants to swap array[0][0] and array[19][0] which is the number 1 and 20 respectively. this is not what i am trying to do. i want to be able to swap 1 and 16, 2 and 17, 3 and 18, 4 and 19, 5 and 20 for the first row. the numbers stay in the same order i am just swapping the rows themselves. then the next row i would want to swap 6 and 11, 7 and 12, 8 and 13, 9 and 14 and 10 and 15. again the numbers stay in their original sequence but the rows themselves are swapped. uhm, if you got an array like that you should probably use array[0][0] to array[4][4]. (makes things alot easier) thus you would swap array[0][0] with array[4][0] , array[0][1] with array[4][1] etc. *** Source Snippet Removed ***