CODEWITHSUNDEEP
cfunctionparameters
user3182162
user3182162

Reputation:

isdigit() in a function

I have a function which takes an integer input by the user.

So I have:

scanf("%d, &x);

And then, the function:

test(int x);

Inside test(), I wanna check if the input is a digit or a character, so I tried:

if (isdigit(x))
    // piece of code
    printf("Done!\n");
else
    printf("Bye!\n");

However, isdigit() does not seem to be working as the program is outputting "Bye!" immediately. What could be the problem?

Thanks.

Upvotes: 1

Views: 1631

Answers (5)

Gil
Gil

Reputation: 1538

The C library function void isdigit(int c ) checks if the passed character is a decimal digit character.

The isdigit() function returns non-zero if c is a decimal digit otherwise 0.The input argument is an int, the value of which the application shall ensure is a character representable as an unsigned char or equal to the value of the macro EOF. i.e ensure that your value is enclosed in single quotes.

You also seemed to have a ; after the if statement which shifts the expected control flow.

char x;  
scanf(" %c", &x); 

if (isdigit(x)) 
  printf("Done!\n");
else 
  printf("Bye!\n");

Upvotes: 1

Grijesh Chauhan
Grijesh Chauhan

Reputation: 58271

You are passing integer not char!

isdigit(x) check whether x is a digit char e.g. '0', '1' but not 0, 1 what you are passing.

It behaves like: 

 isdigit('h')  returns 0
 isdigit('1')  returns 1      
 isdigit(1)  returns 0    // your are passing this

Read manual:

Standard C Library Functions ctype(3C)

isdigit() Tests for any decimal-digit character.

Upvotes: 4

chux
chux

Reputation: 153457

Suspect OP wants to read a char

char x;  // new type
scanf(" %c", &x); // new format specifier

if (isdigit(x))  // remove ;
  // piece of code
  printf("Done!\n");
else if (isalpha(x)) // added test @Joachim Pileborg
  printf("Is a alpha!\n");
else 
  printf("Bye!\n");

Upvotes: 0

thumbmunkeys
thumbmunkeys

Reputation: 20764

remove the semicolon:

if (isdigit(x)); // <===

Because of the semicolon, if it is a digit you execute an empty statement.

Upvotes: 1

egur
egur

Reputation: 7960

isdigit tests a character:

isdigit('5') == true;
isdigit(5) == false;

Upvotes: 1

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