scanf and conversion problem

[yxxxxy]

Hi, this is a part of my program code.
i want to ask two questions.
int time;
float rate;
float salary;

printf("Enter # of hours worked (-1 to end):");
scanf("%d",&time);

while (time!=-1) {
printf("Enter hourly rate of the worker ($00.00):");
1 scanf("%f",&rate);
if (time>=40)
2 salary=(time-40)*3/2*rate+40*rate;
else
salary=time*rate;

printf("Salary is $%.2f\n",salary);

printf("Enter # of hours worked (-1 to end):");
scanf("%d",&time);
}

first question:
there is no error and warning.
but
when i change 3/2 to 1.5 (line 1), it will reveals a
warning :conversion from 'double' to 'float', possible loss of data
why?

second question:
when i change "%f" to " %f",there is no change in result.
but when i change it to "%f " , it will stop at this line .
and when i change it to "% f",it will output a wrong num and not let
me print second time .
why?

my english is not good,if i didn't express my idea clearly ,please
forgive me.

Thank you very much.

[Peter Nilsson]

yxxxxy <[e-mail]:

* Hi, this is a part of my program code.
* i want to ask two questions.

* * * * * * * * int time;
* * * * * * * * float rate;
* * * * float salary;

* * * * printf("Enter # of hours worked (-1 to end):");
* * * * scanf("%d",&time);

* * * * while (time!=-1) {
* * * * * * printf("Enter hourly rate of the worker ($00.00):");
* *1 * * * *scanf("%f",&rate);
* * * * * * * * if (time>=40)
* *2 * * * * * * *salary=(time-40)*3/2*rate+40*rate;
* * * * * * * * * * * * * * * * * * *else
* * * * * * * * * * * * salary=time*rate;

* * * * * * * * printf("Salary is $%.2f\n",salary);

* * * * * * * * printf("Enter # of hours worked (-1 to end):");
* * * * * * scanf("%d",&time);
* * * * }

first question:
there is no error and warning.
but
when i change 3/2 *to 1.5 (line 1), it will reveals a
warning :conversion from 'double' to 'float', possible
loss of data why?

Because multiplying an integer by 3 and dividing by 2
produces an integer. Multiplying an integer by 1.5 will
produce a double (since 1.5 is of type double). As
doubles usually have more precision that floats, the
compiler has decided to warn that you are storing a
double value into a float. [It doesn't have to, but
yours did.]

second question:
when i change "%f" to " %f",there is no change in result.

Read the spec for scanf. All you've done is asked scanf
to ignore optional leading whitespace twice.

but when i change it *to "%f *" , it will stop at
this line .

Because a space is a conversion directive in its own right.
Find out what it is by reading the specs.

and when i change it to "% f",

That is not a valid conversion directive. Undefined
behaviour is allowed to do anything.

Big Tip: C is the worst language to learn by experimentation.

--
Peter

[Pilcrow]

On Wed, 29 Oct 2008 21:16:36 -0700 (PDT), Peter Nilsson
<ai***@acay.com.auwrote:

>
Big Tip: C is the worst language to learn by experimentation.

Amen!

[yxxxxy]

On 10ÔÂ30ÈÕ, ÏÂÎç12ʱ16·Ö, Peter Nilsson <[e-mail]:

yxxxxy <[e-mail]:

Hi, this is a part of my program code.
i want to ask two questions.

int time;
float rate;
float salary;

printf("Enter # of hours worked (-1 to end):");
scanf("%d",&time);

while (time!=-1) {
printf("Enter hourly rate of the worker ($00.00):");
1 scanf("%f",&rate);
if (time>=40)
2 salary=(time-40)*3/2*rate+40*rate;
else
salary=time*rate;

printf("Salary is $%.2f\n",salary);

printf("Enter # of hours worked (-1 to end):");
scanf("%d",&time);
}

first question:
there is no error and warning.
but
when i change 3/2 to 1.5 (line 1), it will reveals a
warning :conversion from 'double' to 'float', possible
loss of data why?

Because multiplying an integer by 3 and dividing by 2
produces an integer. Multiplying an integer by 1.5 will
produce a double (since 1.5 is of type double). As
doubles usually have more precision that floats, the
compiler has decided to warn that you are storing a
double value into a float. [It doesn't have to, but
yours did.]

second question:
when i change "%f" to " %f",there is no change in result.

Read the spec for scanf. All you've done is asked scanf
to ignore optional leading whitespace twice.

but when i change it to "%f " , it will stop at
this line .

Because a space is a conversion directive in its own right.
Find out what it is by reading the specs.

and when i change it to "% f",

That is not a valid conversion directive. Undefined
behaviour is allowed to do anything.

Big Tip: C is the worst language to learn by experimentation.

--
Peter- Òþ²Ø±»ÒýÓÃÎÄ×Ö -

- ÏÔʾÒýÓõÄÎÄ×Ö -

Thank you very much!
And thank your tip!