Struggling to program a simple calculator - c

Question

I am trying to program a simple calculator. Here is my code first:
#include <stdio.h>
#include <stdlib.h>
int main(void) {
char operator = 0;
float num1 = 0.0;
float num2 = 0.0;
float sol = 0.0;
while (operator != 'q') {
printf("Operator: ");
scanf("%c", &operator);
printf("First Number: ");
scanf("%f", &num1);
printf("Second Number: ");
scanf("%f", &num2);
switch (operator)
{
case '+': sol = num1 + num2; break;
case '-': sol = num1 - num2; break;
case '*': sol = num1 * num2; break;
case '/': sol = num1 / num2; break;
case 'q': printf("Finished!"); exit(0);
default: printf("Error!"); exit(0);
}
printf("The solution is: %.2f\n\n", sol);
}
return 0;
}
So for me the code is fine. As you can see I did this with a while loop that lets you calculate until you type in 'q' as operator. The first run of the loop works fine but then it gets creepy (my console):
Operator: +
First Number: 5
Second Number: 4
The solution is: 9.00
Operator: First Number:
Why does the program not let me enter an operator in the second loop run?

Answer 1

Most format specifiers with scanf will skip leading whitespace. %c does not.
scanf("%f", &num2); at the end of the first iteration leaves a newline in the input buffer.
scanf("%c", &operator); at the start of the second iteration, reads the newline and proceeds.
using a space before %c in scanf(" %c", &operator); will allow %c to skip the leading whitespace and capture the operator.

Answer 2

You should check scanf for errors:
#include <stdio.h>
#include <stdlib.h>
int main(void) {
char operator = 0;
float num1 = 0.0;
float num2 = 0.0;
float sol = 0.0;
while (operator != 'q') {
printf("Operator: ");
if((scanf(" %c", &operator)) != 1){
printf("Error, Fix it!\n");
exit(1);
}
printf("First Number: ");
if((scanf("%f", &num1)) != 1){
printf("Error, Fix it!\n");
exit(1);
}
printf("Second Number: ");
if((scanf("%f", &num2)) != 1){
printf("Error, Fix it!\n");
exit(1);
}
switch (operator){
case '+': sol = num1 + num2; break;
case '-': sol = num1 - num2; break;
case '*': sol = num1 * num2; break;
case '/': sol = num1 / num2; break;
case 'q': printf("Finished!"); exit(0);
default: printf("Error!"); exit(0);
}
printf("The solution is: %.2f\n\n", sol);
}
return 0;
}
and as you can see I changed scanf("%c", &operator); to this scanf(" %c", &operator); to make scanf to ignore (skip) Whitespace.