So, I tried this, but program goes out since I click "calculate"

Qt Code: 
  1. #include "widget.h"
  2. #include <QAbstractItemModel>
  3.  
  4. Widget::Widget(QWidget *parent)
  5.     : QWidget(parent)
  6. {
  7.     this->setGeometry(30,30,800,750);
  8.     rank = new QLineEdit("Enter the Rank", this);//rank->setGeometry(10,0,20,20);
  9.     ok = new QPushButton("Ok", this); ok->setGeometry(150, 0,80,30);
  10.     calculate = new QPushButton("calculate",this); calculate->setGeometry(250,0,80,30);
  11.  
  12.  
  13.  
  14.     connect(ok,SIGNAL(clicked()),this,SLOT(ok_clicked()));
  15.     connect(calculate,SIGNAL(clicked()),this,SLOT(calculate_clicked()));
  16. }
  17.  
  18. Widget::~Widget()
  19. {
  20.  
  21. }
  22.  
  23. void Widget::ok_clicked()  
  24. {
  25.  
  26.    rank_of_Matrix = rank->text().toDouble();  
  27.    tbl=new QTableWidget(rank_of_Matrix,rank_of_Matrix,this); 
  28.    tbl->setGeometry(20,50,770,250);  
  29.    tbl->show();                      
  30. }
  31.  
  32. void Widget::calculate_clicked()  
  33. {
  34.     tbl_2  = new QTableWidget(rank_of_Matrix,rank_of_Matrix,this);  
  35.  
  36.     tbl_2 ->setGeometry(20,350,770,250);   
  37.     Action_toArray(); 
  38.     tbl_2 ->show(); 
  39. }
  40.  
  41. void Widget::Action_toArray()
  42. {
  43.  
  44.     A= new float* [rank_of_Matrix];  
  45.     for(int i=0;i<rank_of_Matrix;i++){
  46.         A[i]=new float [rank_of_Matrix];
  47.     }
  48.  
  49. //read from Table 1 tbl
  50.     for(int i=0;i<rank_of_Matrix;i++){
  51.         for(int j=0;j<rank_of_Matrix;j++){
  52.  
  53.            A[i][j] = tbl->item(i,j)-> data(Qt::DisplayRole).toFloat();
  54.         }
  55.     }
  56.  
  57.     //operation with Array 
  58.     for(int i=0;i<rank_of_Matrix;i++){
  59.         for(int j=0;j<rank_of_Matrix;j++){
  60.            if(A[i][j]==2)
  61.            {
  62.                A[i][j]=0;
  63.            }
  64.         }
  65.     }
  66.  
  67.     //write to Table2    tbl_2 
  68.     QVariant tableData;
  69.     for(int i=0;i<rank_of_Matrix;i++){
  70.         for(int j=0;j<rank_of_Matrix;j++){
  71.          tableData = A[i][j];
  72.          tbl_2->item(i,j)->setData(Qt::EditRole,tableData);
  73.         }
  74.     }
  75. }
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So, could you please tell me what is wrong and how I can fix it?