Assigning a value to a specific column in a multidimensional array (C)

Question

I'm trying to find a way to assign a specific column to a specific value in a multidimensional array

Per below, I'm aware of how to assign it manually and through a for loop.

Is there an easier way to go about doing it? thanks

#include < stdio.h >
double Test1[4][5];
double a0, a1, a2, a3;

int main() {
  //Assigning one column in a specific row manually
  Test1[1][1] = 1;
  a0 = Test1[0][1];
  a1 = Test1[1][1];
  a2 = Test1[2][1];
  a3 = Test1[3][1];

  printf("a0  %f \r\n", a0);
  printf("a1  %f \r\n", a1);
  printf("a2  %f \r\n", a2);
  printf("a3  %f \r\n", a3);

  int row = sizeof(Test1) / sizeof(Test1[0]);
  printf("rows  %d \r\n", row);
  int column = sizeof(Test1[0]) / sizeof(Test1[0][0]);
  printf("cols  %d \r\n", column);

  int L;
  double a;
  //Assigning one column in all rows to one
  for (L = 0; L < row; L = L + 1) {
    Test1[L][1] = 1;
  }

  a0 = Test1[0][1];
  a1 = Test1[1][1];
  a2 = Test1[2][1];
  a3 = Test1[3][1];

  printf("a0  %f \r\n", a0);
  printf("a1  %f \r\n", a1);
  printf("a2  %f \r\n", a2);
  printf("a3  %f \r\n", a3);

  return 0;
}

Answer 1

There is no standard function that sets a column of a 2D array. In C, multidimensional arrays are a bit of an illusion; they compile into 1D arrays. Here is some code to demonstrate that the values unwind into a 1D array:

#include <stdio.h>

int main(){
    int test[10][2] = {0};
    //point to the 1st element
    int * p1 = &test[0][0];

    //20th position is the 9th row, 2nd column
    p1[19] = 5;

    //9th element is the 5th row, 1st column
    int * p2 = p1 + 8;
    *p2 = 4;

    printf("Value set to 5: %d\n",test[9][1]);
    printf("Value set to 4: %d\n",test[4][0]);
}