Pascal allows using one loop inside another loop. Following section shows few examples to illustrate the concept.
The syntax for a nested for-do loop statement in Pascal is as follows:
for variable1:=initial_value1 to [downto] final_value1 do begin for variable2:=initial_value2 to [downto] final_value2 do begin statement(s); end; end;
The syntax for a nested while-do loop statement in Pascal is as follows:
while(condition1)do begin while(condition2)do begin statement(s); end; statement(s); end;
The syntax for a nested repeat ... until loop Pascal is as follows:
repeat statement(s); repeat statement(s); until(condition2); until(condition1);
A final note on loop nesting is that you can put any type of loop inside of any other type of loop. For example a for loop can be inside a while loop or vice versa.
The following program uses a nested for loop to find the prime numbers from 2 to 50:
program nestedPrime; var i, j:integer; begin for i :=2 to 50 do begin for j :=2 to i do if(i mod j)=0 then break;{*if factor found,not prime *} if(j = i)then writeln(i ,' is prime'); end; end.
When the above code is compiled and executed, it produces following result:
2 is prime 3 is prime 5 is prime 7 is prime 11 is prime 13 is prime 17 is prime 19 is prime 23 is prime 29 is prime 31 is prime 37 is prime 41 is prime 43 is prime 47 is prime