//=========================================== // CodeName : Filling a matrix using for loop // Done for : Randeep Singh // By : Babak Sheykhan // Created : Nov 10, 2017 // Modified : Nov 10, 2017 // // Input tip: You don't need to input anything //============================================ #include #include // setw() #include // srand(), rand() #include // time() using std::cout; using std::cin; using std::endl; int main() { /////////////////////////////////////////// // Seeds the pseudo-random number generator // Note from "cppreference": // Standard practice is to use the result of a call to time(0) as the seed. // However, time() returns a time_t value, and time_t is not guaranteed to be // an integral type. In practice, though, every major implementation defines // time_t to be an integral type, and this is also what POSIX requires. // // My own preference to do so is like the below. // "static_cast(expresion)" is a kind of typecast operator which is better // than c-style cast [ srand((unsigned)time(0)) ]. Although it's ugly! srand(static_cast(time(0))); ////////////////////////////// // A 3 * 3, 2D array (matrix). // It's going to be filled with random numbers. int matrix[3][3]; /////////////////// // Write to matrix: // These 2 for loops are responsible to loop through // the matrix and provide posibility to access and fill // each element of that in the range [-20, 20] // // i represents row and j column. // initial state of the matrix // // | 0 0 0 | // | 0 0 0 | // | 0 0 0 | // //////////////// // i = 0, j = 0 // v // >| x 0 0 | // | 0 0 0 | // | 0 0 0 | // // // i = 0, j = 1 // v // >| x x 0 | // | 0 0 0 | // | 0 0 0 | // // // i = 0, j = 2 // v // >| x x x | <- 1st row done // | 0 0 0 | // | 0 0 0 | // //----------------- // i = 1, j = 0 // v // | x x x | // >| x 0 0 | // | 0 0 0 | // // // i = 1, j = 1 // v // | x x x | // >| x x 0 | // | 0 0 0 | // // // i = 1, j = 2 // v // | x x x | // >| x x x | <- 2nd row done // | 0 0 0 | // //---------------- // // i = 2, j = 0 // v // | x x x | // | x x x | // >| x 0 0 | // // // i = 2, j = 1 // v // | x x x | // | x x x | // >| x x 0 | // // // i = 2, j = 2 // v // | x x x | // | x x x | // >| x x x | <- 3rd row done // for (int i = 0; i < 3; ++i) { for (int j = 0; j < 3; ++j) { /////////////////////////////////////////////////// // Filling the current element of matrix defined by // i and j with a random number between -20 to 20. matrix[i][j] = rand() % 41 + (-20); //////////////////////////////////////////////// // putting 6 rooms befor printing each elements. cout << std::setw(6) << matrix[i][j]; } cout << endl; } }

[Tut]@RandeepSingh_forLoopMatrix