How to picture "for" loop in block representation of algorithm

What's a "block scheme"?

If I were drawing it, I might draw a box with "for each x in y" written in it.

If you're drawing a flowchart, there's always a loop with a decision box.

Nassi-Schneiderman diagrams have a loop construct you could use.

Here's a flow chart that illustrates a for loop:

The equivalent C code would be

for(i = 2; i <= 6; i = i + 2) {
    printf("%d\t", i + 1);
}

I found this and several other examples on one of Tenouk's C Laboratory practice worksheets.