I see there are some conditional errors(consider a case,if your testscore is 95 then what will be the grade?because all conditions true for it) in your if else conditions..it will work better just like as it..
if(testscore >= 90 )
else if((testscore >= 80 ) && (testscore < 90))
else if((testscore >= 70 ) && (testscore < 80))
else if((testscore >= 65 ) && (testscore < 70))
there are also some syntax errors which is informed you earlier by lewax00..