尝试相乘矩阵。得到荒谬的结果

Question

#include <iostream>

#include <malloc.h>

using namespace std;


int main()

{
 int r,c,r2,c2;
 cout << "Enter the number of rows:- \n";
 cin >> r;
 cout << "\n" <<"Enter the number of columns: \n";
 cin >> c;
 int **mat;
 int **mat2;
 mat=(int**)malloc(sizeof(int)*r);  // allocating memory to a row
 for (int i=0;i<r;i++)
   {
      *(mat+i)=(int*)malloc(sizeof(int)*c);  /* allocating memory to 
                           columns in rows ( double pointers ) */
   }
cout << "\n\n" << "Please enter the 1st matrix of order:- " << r << 'x' 
     << c<< endl;

for (int i=0;i<r;i++)
    { for (int j=0;j<c;j++)
       {
           cin >> *(*(mat+i)+j);
           cout << endl;
       }
    }
cout << "Enter the number of rows(2nd):- \n";
cin >> r2;
cout << "\n" <<"Enter the number of columns(2nd): \n";
cin >> c2;
mat2=(int**)malloc(sizeof(int)*r2);
for (int i=0;i<r2;i++)
   {
     *(mat2+i)=(int*)malloc(sizeof(int)*c2);
   }
cout << "\n\n" << "Please enter the 2nd matrix of order:- " << r2 << 'x' 
     << c2 <<endl;

for (int i=0;i<r2;i++)
  {
    for (int j=0;j<c2;j++)
     {
        cin >> *(*(mat2+i)+j);
        cout << endl;
     }
  }
cout <<"\n\n\n" <<"The 1st matrix you entered is:- \n";

for (int i=0;i<r;i++)
  {  for (int j=0;j<c;j++)
     {
     cout << *(*(mat+i)+j) << '\t';
     }
     cout << endl;
  }
cout << "\n\n" << "The second matrix you entered is:- \n";

for (int i=0;i<r2;i++)
 {  for (int j=0;j<c2;j++)
       {
            cout << *(*(mat2+i)+j) << '\t';
       }
    cout << endl;
}

int **mat4;
mat4=(int**)malloc(sizeof(int)*r);

for (int i=0;i<r;i++)
   {
      *(mat4+i)=(int*)malloc(sizeof(int)*c2);
   }
if (c!=r2)
   {
      cout << "\n\n These two matrices cannot be multiplied as number of 
             columns("<< c<< ")of 1st matrix \nis not equal to number of 
             rows("<< r2<< ") of second matrix."; 
   }
if( c==r2)
 {
   for (int i=0;i<r;i++)
      {
       for (int z=0;z<c2;z++)
           { 
             for (int j1=0;j1<r2;j1++)
              {
               mat4[i][z]+= mat[i][j1] * mat2[j1][z]; /* logic to 
                                          multiply two matrices */
              }
           }

     }
  for (int i=0;i<r;i++)
      {
       for (int j=0;j<c2;j++)
          {
            cout <<  mat4[i][j] << '\t';
          } 
        cout << endl;
      }
  }
 return (1);
}

当我输入2x2和2x3矩阵或c2 = c + 1的任何组合时，就会出现问题。我在输出中得到随机大数。否则，如果我输入行数和列数的任何其他组合，则效果很好。例如-如果我把r2 = 3和c2 = 4放进去，无论我做什么输入，我都会在第1列和第3列得到荒谬的值。