Invalid types int[int] for array subscript. Searching in a matrix

Question

I have been trying to do a binary search in a matrix and getting this error
Here's the code

#include <iostream>
using namespace std;
int count = 0;

int search(int r, int c , int key , int * matrix){
int row=0;
int col=c-1;
while(row<c && col>=0){
if(count>0) break;
if(matrix[row][col]==key){
cout<<"Key is at "<<row<<","<<col<<endl;
count++;
} else if(matrix[row][col]<key){
row++;
} else{
col--;
}
} return -1;
}

int main(){
int r; // Get length of row from user
cout<<"Enter the row number \n";
cin>>r;
int c; // Get length of col from user
cout<<"Enter the col number \n";
cin>>c;

int matrix[r][c]; // a matrix is defined of r x c
cout<<"Enter the values of matrix \n";
// Nested loop to get the value of matrix from user
for(int i=0;i<r;i++) {
for(int j=0;j<c;j++){
cin>>matrix[i][j];
}
}
int key;
cin>>key;
search(r,c,key,(int*)matrix);
return 0;
}

Answer 1

that's Inplace of matrix[row][col] in function.

Answer 2

Use pointer notation of accessing array elements as
*((matrix+row*r)+col) ;

Or
Define function as

const int M = 5;
int search(int r, int cr, int key , int (*matrix)[M] )
{
//..
}

Call function as :

search(r,c,key, matrix);

Answer 3

Thanks it worked 🙏 can you please explain what you did there..

Answer 4

Sir can you guide me on which line I have to use the first solution?

Answer 5

You are passing first array element address (int*)matrix;

*(*(matrix+row)+col) is equal to martix[row][col]; in pointer notation.

*((matrix+row*r) +col) here (matrix+row*r) will point to r'th row directly..
hope it helps..