The question is vague. They said they have input as 1234 but how this input is being provided?
Inside main there is no input available to support the string entered.
In the function definition itself:
a-> If the input is passed in the parameter then char a declaration is invalid.
b-> If the input is passed in the char a itself then we can't simply pass the value as 1234 with the given declaration. Because 1234 will be a string. But the given program simply declares a character variable a. All values needs to be entered one by one. But again no looping mechanism is given.
Now considering the fact that the input 1234 is given one by one then for the given input we can only pass 1 as the input as after that the program will terminate and in doing so we will get "no output in the answer". Hence option B.
Here's an image of what points I am trying to make:
and if the values are provided one by one.
We are getting a blank screen as an output.
Please note that this answer is limited only up to my understandings. Please correct me if there's something wrong.