Please let me know if there is a way to get the first address of any line of a two-dimensional array "quickly."

(I was confused about the multiplication time.Please see 774RR's response.)

Suppose you have a large array of about 1000 x 1000 (such as an image).iTo get the first address on the line,

double lightness[1000][1000];
  // ...
  long i = 200; // where i = 200
  double*pLightness=lightness[i];   

If you repeat this for i from 0 to 999, the more i, the more time it takes to get an address.(Because of the [] specification)

for(i=0;i<1000;i++){
    * pLightness=lightness[i]; // The first address in line i
    // ... (Working with Addresses
  }

Is there a faster way to get the first address of the i line of the matrix from i=0 to 999?
"If possible, I wish there was a faster and more elegant way than ""pLightness+=1000""…

The motivation for the question is that if you get an address in the i row j column, you can get an address in the right-next, i row j+i column by increasing the pointer containing the address.

//(i,j)=(300,0) to (300,999) using the address pLightness of lightness[i][j]
  i = 300;
  pLightness=lightness[i]; // The first address on line 300
  for (long j=0; j<1000;j++, pLightness++) {
    // ... (Working with Addresses
  }

Well, it's a basic question, so you might be asking me to read a reference book or use my brain a little more, but please forgive me.