During my task two `Loop through matrix and add up all the elements. Assign your answer to the sum variable.`

, my code

for (int i = 0; i < row;i++){
for (int j = 0; j < col;j++){
int num = matrix[i][j];
sum += num;
}
}

is not accepted, what is the difference between my code and official solution ?

for (int i = 0; i < row;i++){
for (int j = 0; j < col;j++){
sum += matrix[i][j];
}
}