Check user input in C with scanf() - c

Question

Purpose:
If user input b is a float number prints floor(b), round(b), ceil(b).
Else prints scanf error: (%d)\n.
The instruction (provided by our teacher) has a code like this, which I don't understand.
Here's my code:
`
#include <stdio.h>
#include <math.h>
int main(void) {
float b;
printf("Eneter a float number");
int a=0;
a=5;
a=scanf("%d", &b);
if (a=0)
{
printf("scanf error: (%d)\n",a);
}
else
{
printf("%g %g %g",floor(b), round(b), ceil(b));
}
return 0
}

Answer 1

Mistake # 1
if (a=0) // condition will be always FALSE
must be
if (a==0)
or better
if (0 == a)
Mistake # 2
scanf("%d", &b); // when b is float
instead of
scanf("%f", &b);
UPDATE:
Actually, for case of checking results of scanf I personally prefer to use != with number of values entered with the last scanf. E.g. if two comma separated integers required to continue calculation snippet can be:
int x, y;
int check;
do{
printf("Enter x,y:");
check = scanf("%d,%d", &x, &y); // enter format is x,y
while(getchar()!='\n'); // clean the input buffer
}while(check != 2);
that loop will re-ask for input if check is not 2, i.e. if it is 0 (when even the first value is incorrect, e.g. abc,12) or if it is 1 (when user forgot comma or enter not a number after comma, e.g. 12,y

Answer 2

Code with corrections and comments - also available here - http://ideone.com/eqzRQe
#include <stdio.h>
#include <math.h>
int main(void) {
float b;
// printf("Eneter a float number");
printf("Enter a float number"); // Corrected typo
fflush(stdout); // Send the buffer to the console so the user can see it
int a=0;
// a=5; -- Not required
a=scanf("%f", &b); // See the manual page for reading floats
if (a==0) // Need comparison operator not assignemnt
{
printf("scanf error: (%d)\n",a); // A better error message could be placed here
}
else
{
printf("%g\n", b); // Just to check the input with ideone - debugging
printf("%g %g %g",floor(b), round(b), ceil(b));
}
return 0; // You need the semi-colon here
}
For VenuKant Sahu benefit
Return Value
These functions return the number of input items successfully matched
and assigned, which can be fewer than provided for, or even zero in
the event of an early matching failure.
The value EOF is returned if the end of input is reached before either
the first successful conversion or a matching failure occurs. EOF is
also returned if a read error occurs, in which case the error
indicator for the stream (see ferror(3)) is set, and errno is set
indicate the error.