用c++语言编写面向小学1~2年级学生，随机选择两个整数和加减法形成算式要求学生解答。

功能要求：

（1）电脑随机出10道题，每题10分，程序结束时显示学生得分；

（2）确保算式没有超出1~2年级的水平，只允许进行50以内的加减法，不允许两数之和或之差超出0~50的范围，负数更是不允许的；

（3）每道题学生有三次机会输入答案，当学生输入错误答案时，提醒学生重新输入，如果三次机会结束则输出正确答案；

（4）对于每道题，学生第一次输入正确答案得10分，第二次输入正确答案得7分，第三次输入正确答案得5分，否则不得分；

（5）总成绩90以上显示“SMART”,80-90显示“GOOD”，70-80显示“OK”,60-70显示“PASS”，60以下“TRY AGAIN”。



-　With c++ language for primary school students in grades 1-2, randomly selected two integers and addition and subtraction formation formula requires students to answer.

Functional requirements:

(1) the computer randomly out of 10 questions, 10 points for each question, the end of the program shows the student score

(2) to ensure that the formula does not exceed the level of 1 to 2, only allowed within 50 of the addition and subtraction, does not allow the sum of the two or more than 0 to 50 range, the negative is not allowed

(3) each question students have three opportunities to enter the answer, when students enter the wrong answer, to remind students to re-enter, if the end of the three opportunities to output the correct answer

(4) for each question, the students first enter the correct answer was 10 points, the second time the correct answer was 7 points, the third time the correct answer was 5 points, or not score

(5) Total score above 90 shows　SMART , 80-90 shows　GOO