visual c++ - C++ Object reference not set to an instance of an object -

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when try compile following program says "build failed. object reference not set instance of object" . i'm kinda new c++ if can me it'll great . i'm trying out example saw in book don't know whats wrong .

using namespace std;  class matrix {     int m[3][3];      public:         void read(void);         void display(void);          friend matrix trans(matrix); }  void matrix :: read(void) {     cout<<"enter elements of 3x3 array matrix : \n";     int i,j;     for(i=0;i<3;i++)     {         for(j=0;j<3;j++)         {             cout<<"m["<<i<<"]["<<j<<"] =";             cin>>m[i][j];         }     } }  void matrix :: display(void) {     int i,j;     for(i=0;i<3;i++)     {         cout<<"\n";         for(j=0;j<3;j++)         {             cout<<m[i][j]<<"\t";         }     } }  matrix trans(matrix m1) {     matrix m2;     int i,j;     for(i=0;i<3;i++)     {         for(j=0;j<3;j++)         {             m2.m[i][j] = m1.m[j][i];         }     }     return(m2);             //returning object }  int main() {     matrix mat1,mat2;     mat1.read();     cout<<"\nyou entered following matrix :";     mat1.display();      mat2 = trans(mat1);     cout<<"\ntransposed matrix :";     mat2.display();      getch();     return 0; }

1 - insert semi-colon after class definition
2 - insert correct headers 

   #include <iostream>    #include <conio.h>

3 - try getting compiler bit more descriptive regards errors. did mentioned , program ran. try it


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