Cal.c

int main()
{
	int N;
	double input;
	
	printf("學號後五碼:30023\n");
	printf("Enter a number:");
	scanf("%lf",&N); //讀double要用%lf
  fflush(stdin);
    
	if(N>=-50 && N<=50)
	{
		printf("輸入運算符號:");
		scanf("%c",&input);

		switch(input)
		{	
			case'+':
				printf("30023+%lf=%lf",N,30023+N);
				break;
			case'-':
				printf("30023-%lf=%lf",N,30023-N);
				break;
			case'*':
				printf("30023*%lf=%lf",N,30023*N);
				break;
			case'/':
				printf("30023/%lf=%lf",N,30023/N);
				break;
		}
	}
  else printf("error");
  
	printf("\n");
	system("pause");
	return 0;
}