Boolean flag = true;        while (flag) {            char a ;            float number1,number2,result = 0;            printf("a表示加法\n");            printf("b表示减法\n");            printf("a表示乘法\n");            printf("d表示除法\n");            printf("q表示退出\n");            printf("请输入您的选择:");            scanf("%c",&a);            switch (a) {                case ‘a‘:                    printf("请输入第一个数：\n");                    scanf("%f",&number1);                    printf("请输入第二个数：\n");                    scanf("%f",&number2);                    result = number1 + number2;                    printf("%.1f + %.1f = %.1f\n",number1,number2,result);                    break;                case ‘b‘:                    printf("请输入第一个数：\n");                    scanf("%f",&number1);                    printf("请输入第二个数：\n");                    scanf("%f",&number2);                    result = number1 - number2;                    printf("%.1f - %.1f = %.1f\n",number1,number2,result);                    break;                case ‘c‘:                    printf("请输入第一个数：\n");                    scanf("%f",&number1);                    printf("请输入第二个数：\n");                    scanf("%f",&number2);                    result = number1 * number2;                    printf("%.1f + %.1f = %.1f\n",number1,number2,result);                    break;                case ‘d‘:                    printf("请输入第一个数：\n");                    scanf("%f",&number1);                    printf("请输入第二个数：\n");                    scanf("%f",&number2);                    result = number1 / number2;                    printf("%.1f + %.1f = %.1f\n",number1,number2,result);                    break;                                    case ‘q‘:                    flag = false;                    printf("已经退出了");                    break;                                    default:                                     break;            }