String Comparison

Question

I have one text box. If anybody enters value like <,>,create,drop etc,The error message will come. I need To avoid that.Also My Visual studio software does not support Valiation controls like regular expression validtor,required field validatr etc,So I cant use regular expression validatior to avoid this sql injection B'coz of this reason I decide to use string comparison to check the textbox value charrecter by charrecter . so I can find out the illegal symbols which entered in the text box. Then I can display the error message... Can anybody help me???