SystemVerilog foreach loop

SystemVerilog arrays are data structures that allow storage of many values in a single variable. A foreach loop is only used to iterate over such arrays and is the easiest and simplest way to do so.

Syntax

The foreach loop iterates through each index starting from 0. If there are multiple statements within the foreach loop, they have to be enclosed with begin and end keywords like all other procedural blocks.

	foreach(<variable>[<iterator>])
		// Single statement
		
	foreach(<variable>[<iterator>]) begin
		// Multiple statements
	end

Example #1: Single dimensional Arrays

module tb;
	int array[5] = '{1, 2, 3, 4, 5};
	int sum;
	
	initial begin
		// Here, "i" is the iterator and can be named as anything you like
		// Iterate through each element from index 0 to end using a foreach
		// loop.
		foreach (array[i])
			$display ("array[%0d] = %0d", i, array[i]);
		
		// Multiple statements in foreach loop requires begin end
		// Here, we are calculating the sum of all numbers in the array
		// And because there are 2 statements within foreach there should
		// be a begin-end
		foreach (array[l_index]) begin
			sum += array[l_index];
			$display ("array[%0d] = %0d, sum = %0d", l_index, array[l_index], sum);
		end
	end
endmodule

ncsim> run
array[0] = 1
array[1] = 2
array[2] = 3
array[3] = 4
array[4] = 5
array[0] = 1, sum = 1
array[1] = 2, sum = 3
array[2] = 3, sum = 6
array[3] = 4, sum = 10
array[4] = 5, sum = 15
ncsim: *W,RNQUIE: Simulation is complete.

Note that foreach is just a shorter version to the following for loop:

	for (int i = 0; i < $size(array); i++) begin
		// Statements inside the for loop
	end

Example #2: Multidimensional Arrays

module tb;
  int md_array [5][2] = '{'{1,2}, '{3,4}, '{5,6}, '{7,8}, '{9,10}};
	
	initial begin
      // First iterate through the first dimension using "i"
      foreach (md_array[i])
        // For each element in first dimension "i", iterate through the
        // second dimension using "j"
        foreach (md_array[i][j])
          $display("md_array[%0d][%0d] = %0d", i, j, md_array[i][j]);      
	end
endmodule

ncsim> run
md_array[0][0] = 1
md_array[0][1] = 2
md_array[1][0] = 3
md_array[1][1] = 4
md_array[2][0] = 5
md_array[2][1] = 6
md_array[3][0] = 7
md_array[3][1] = 8
md_array[4][0] = 9
md_array[4][1] = 10
ncsim: *W,RNQUIE: Simulation is complete.