calculator output in c - c

Question

I made a simple calculator program using switch case, but the output is different than I expected.
int main(){
double a, b;
double sum = 0;
char o; //operator
printf("Enter operator\n");
scanf("%c", &o);
printf("Enter first operand\n");
scanf("%f", &a);
printf("Enter second operand\n");
scanf("%f", &b);
switch (o)
{
case '+':
sum = a + b;
break;
case '-':
sum = a - b;
break;
case '*':
sum = a * b;
break;
case '/':
sum = a / b;
break;
if (b == 0){ printf("Error"); }
break;
}
printf("The result is\n%10.10lf\n", sum);
getchar();
getchar();
}
The result of 'sum' is some huge astronomical numbers. Can someone tell why?

Answer 1

Try %lf instead of %f because that way you will have a and b as the type double rather than float.

Answer 2

a and b are both of type double. The correct format specifier for double in scanf is %lf, not %f (which is for float).
scanf("%lf", &a);
Note that in printf, %f is used or for double (the same for float because it's promoted to double). Since C99, %lf in printf is the same as %f.

Answer 3

you are trying to convert double to float which is not implicitly possible inside scanf or printf function. What scanf was doing, It was purging/reformatting the whole (double)input into an empty float value. Here is working one :
#include<stdio.h>
int main(){
double a, b;
double sum = 0;
char o; //operator
printf("Enter operator\n");
scanf("%c", &o);
printf("Enter first operand\n");
scanf("%lf", &a);
printf("Enter second operand\n");
scanf("%lf", &b);
switch (o)
{
case '+':
sum = a + b;
break;
case '-':
sum = a - b;
break;
case '*':
sum = a * b;
break;
case '/':
sum = a / b;
break;
if (b == 0){ printf("Error"); }
break;
}
printf("The result is\n %f\n", sum);
}

Answer 4

As everyone has pointed out, you need scanf ("%lf", &a); and same for b.
Now in your switch statement you wanted to prevent division by zero :
case '/':
sum = a / b;
break;
if (b == 0){ printf("Error"); }
break;
But what happens there is that you break; before getting to the condition. Suppose we removed that first break; the division by zero is still performed before you print the error message anyway.
One way to prevent division by zero would be :
case '/':
if (b)
sum = a / b;
else
printf("Error");
break;
where we check that b != 0 before we make the division and then we either divide or print the error message.