How many cups is 200g of icing sugar?

That would depend on the type of sugar. I have included charts to help you convert the 3 most common types of sugar from grams to cups.

Granulated (common) Sugar

1/8 cup = 30 grams
1/4 cup = 55 grams
1/3 cup = 75 grams
3/8 cup = 85 grams
1/2 cup = 115 grams
5/8 cup = 140 grams
2/3 cup = 150 grams
3/4 cup = 170 grams
7/8 cup = 200 grams
1 cup = 225 grams

Confectioners' (powdered) Sugar

1/8 cup = 15 grams
1/4 cup = 30 grams
1/3 cup = 40 grams
3/8 cup = 45 grams
1/2 cup = 60 grams
5/8 cup = 70 grams
2/3 cup = 75 grams
3/4 cup = 85 grams
7/8 cup = 100 grams
1 cup = 110 grams

Brown Sugar

1/8 cup = 25 grams
1/4 cup = 50 grams
1/3 cup = 65 grams
3/8 cup = 75 grams
1/2 cup = 100 grams
5/8 cup = 125 grams
2/3 cup = 135 grams
3/4 cup = 150 grams
7/8 cup = 175 grams
1 cup = 200 grams