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]

  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.

 

[Pilcrow]

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

Amen!

 

[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?

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.

Thank you very much!
And thank your tip!