Thread: why won't this code compile?

#include <stdio.h>




unsigned int getInputData(){
unsigned int digit;
printf("Please Enter in a positive number, then hit ENTER\n");



if (scanf("%d", &digit) !=1){
printf("That is not an integer\n");
return(-1);}
else if (sizeOf(digit)>4){
printf("That integer is way too large!");
return(-1);}
else
printf("Good, you've entered an integer!");
printf("The number you entered is: %d\n", digit);
return(digit);
}

int main(void){

getInputData();
return(0);
}

I get the following errors

/tmp/ccKpU3tT.o: In function `getInputData':
/tmp/ccKpU3tT.o(.text+0x63): undefined reference to `sizeOf'
collect2: ld returned 1 exit status

I dont' get it...please help!