Thread: Calculator

Hi, I would like to create a C program which requires the input in this form: number1 operator number2, where number1 and number2 are numbers of type double and operator is one of the characters +,-,*,/.

There is my attempt to write this code:

Code:

#include <stdio.h>

double main()
{
   char operator;
   double num1, num2;


   printf("Type what you want to calculate\n");
   scanf("%d%c%d", &num1, &operator, &num2);


   switch(operator);
   {
	case '+':
		printf("num1+num2=%.2f",num1+num2);
		break;
	case '-':
		printf("num1-num2=%.2f",num1-num2);
		break;
        case '*':
		printf("num1*num2=%.2f",num1*num2);
		break;
	case '/':
		if(num2 != 0)
		{
                	printf("num1/num2=%.2f",num1/num2);
			break;
		}
		else
		{
			printf("Error! operator is not correct");
			break;
		}
	default:
		printf("Error! operator is not correct");
		break;
   }
   return 0;
}

Now I have to solve these problems:

1. This code above doesn't work and I don't know why.
2. I don't know how to fix the case when some user enters the input in this form:
   Code:

   1.5896        *5

   or
   Code:

   7    /       5

   I mean how the program knows that
   Code:

   1.5896        *5

   is the same as
   Code:

   1.5896*5

3. I don't know how to fix the case when the user enters the input in the incorrect form for example
   Code:

   3

I am a beginner in C, please take note of this while explaining.
Thanks

1) lookup the ways in which you can accept data from stdin from the manual.
2) if you really want to code - given that we know the valid characters you can receive from stdin, i.e. 0 thru 9, +, -, *, / and .(dot)... we know what to do for each character

Your code looks fairly good.

"%lf" is the correct format specifier for reading in a double with scanf. You can see this by looking at the scanf documentation (scanf - C++ Reference). There are also more options which may allow you to do some of the other things that you wish to do.

Code:

double main()

I guess you thought that you should change this to a double because you are working to double instead of ints. This is not correct. It should always be

Code:

int main( void )

until you know better.