How to re initialize variable (CCS 102)(Program C) - c

Question

after making progress and rewriting most of the code for our calculator project, i run into a problem.
as the title suggest i need help with reinitializing the variable after loop or in every loop.
problem:
It should to like this:
as you can see instead of prompting an error it still calculate, suggesting that the inputed int was stored in my variable. which i maybe wrong or something but if i cannot fix these i make more progress.
Here is the code:
#include <stdio.h>
#include <stdbool.h>
//bool function
bool isInteger(double val)
{
int truncated = (int)val;
return (val == truncated);
}
int main(int argc, char *argv[])
{
//local variable
double a, b;
char operation, option = 'y';
//loop
while(option == 'y' || option == 'Y')
{
//system("cls");
printf("Enter number and operator to solve:\n\nExapmple [a + b][a - b][a * b][a / b]\n");
scanf("%lf %c %lf", &a, &operation, &b);
// nested if
if(isInteger(a) && isInteger(b))
{
if(operation == '+')
{
printf("Result: %.1lf\n\n", a + b); //ouput result
}
else if(operation == '-')
{
printf("Result: %.1lf\n\n", a - b); //ouput result
}
else if(operation == '*')
{
printf("Result: %.1lf\n\n", a * b); //ouput result
}
else if(operation == '/')
{
printf("Result: %.1lf\n\n", a / b); //ouput result
}
else
{
//output error
printf("Invalid Operater!\n");
}
}
else
{
//output error
printf("Input is not a digit!\n");
}
//output selection
printf("Do you want to retry [y]/[n]?");
option = getch(); //not recommended but just a small project
//scanf("%c", &option); -- stops the loop
} //end loop
}

Answer 1

In your second example (i.e., second time around), this line
scanf("%lf %c %lf", &a, &operation, &b);
tries to read an a into a double which will cause scanf to fail and return early.
Check the documentation of scanf and you'll see that it returns the number of values read and will set errno on failure. These must be checked before a, operation and b can be safely used.