Isalpha is requiring an identifier - c

Question

Here's my code:
#include <stdio.h>
#include <ctype.h>
main(){
float input;
printf("Input: ");
scanf("%f", &input);
if (isalpha(input) || (input) < 0)){
printf("Input is an alphabet or is lesser than 0");
} else {
printf("Input is correct. %f is a number larger than 0", input);
}
}
I want the code to detect if input is a number larger than 0, or is it an alphabet. However, I am getting this error:
8: error: identifier expected
What does it mean to my code's execution? How am I supposed to run the code successfully?

Answer 1

Correct parentheses in if:
if ( isalpha(input) || (input < 0) )
In addition, you need to check the return value of scanf() whether there was input or not. In the case of no input, the return value would be 0 or in case of multiple inputs how many succeeded. In your case, you can use the return value to determine whether a float was input or not.
The main() should return an int and always initialize your variables.
Example (live):
#include <stdio.h>
#include <ctype.h>
int main()
{
float input = 0.0f;
printf("Input: ");
int ret = scanf("%f", &input);
if ( ret == 0 )
{
printf("ERROR: Input is NOT a float!\n");
return -1;
}
if ( input < 0.0f )
{
printf("Input is less than 0");
}
else
{
printf("Input is correct. %f is a number larger than 0", input);
}
return 0;
}

Answer 2

Your parentheses aren't opened/closed properly.
Maybe your ide/compiler is taking care of it, but it should be int main()
isalpha() will behave unexpectedly with float values. Try avoiding that.

Answer 3

First of all you are missing int declaring main,
int main()
Also,you have excessive bracket in line
if (isalpha(input) || (input) < 0)){
Scanf uses %f to read floats. What your program will do is accept any ascii character and I suppose that wasn't your intention.

Answer 4

I am still not sure what you need, but you could try something like this as a starting point. It does not handle all possible inputs, and will erroneously classify an input such as #42 as alphabet or lesser than 0, which is questionable, but you can iterate on this and hopefully get to a more polished version.
#include <stdio.h>
#include <ctype.h>
int main(){
float input;
printf("Input: ");
if (scanf("%f", &input) && input >= 0){
printf("Input is correct. %f is a number larger than 0", input);
} else {
printf("Input is an alphabet or is lesser than 0");
}
}
Explanation
We save the value in input, if compatible with the %f format:
float input;
Prompt for the user:
printf("Input: ");
This condition is made of two parts; the first part is the scanf, that will try to read input, and if successful will evaluate to 1, which is true, so the second part input >= 0 will be evaluated, and if input is indeed >= 0 we print the first message.
if (scanf("%f", &input) && input >= 0){
printf("Input is correct. %f is a number larger than 0", input);
Else we print the second message.
} else {
printf("Input is an alphabet or is lesser than 0");
}