我想用for循环做一些事情

Question

i want to make something use loop for like this

1 1 1 1
1 1 1 2
1 1 1 3
1 1 2 1
1 1 2 2
1 1 2 2
1 1 2 3

i have tried something like this ,but it comes out fail

for ($i=1; $i <=3 ; $i++) { 
            # code...
            echo "a$i";
            for ($i=1; $i <=3 ; $i++) { 
                # code...
                echo "b$i";
                for ($i=1; $i <=3 ; $i++) { 
                    # code...
                    echo "c$i";
                    for ($i=1; $i <=3 ; $i++) { 
                        # code...
                        echo "d$i";
                    }
                }
            }
        }

hope someone can help, thanks

Answer 1

You must use different counter on each nested loop. You cannot use the same variable at the same time. Also, your echoing a string with the variable in the wrong way (lacks concatenation)

Try

for ($i=1; $i <=3 ; $i++) { 
        # code...
        echo "a ".$i;
        for ($j=1; $j <=3 ; $j++) { 
            # code...
            echo "b ".$j;
            for ($k=1; $k <=3 ; $k++) { 
                # code...
                echo "c ".$k;
                for ($m=1; $m <=3 ; $m++) { 
                    # code...
                    echo "d ".$m;
                }
            }
        }
    }