Beginner-need help

hello, i'm a beginner in C programming
i need some help about C.

Code:

---

#include <stdio.h>
#include <stdlib.h>

int main()
{
    float av,prc,i,j,k;
    scanf("%f %f %f", &i, &j, &k);
    mak(&i,&j,&k,&av,&prc);
    printf("\n%f %f",av,prc);
    return 0;
}

mak(float a, float b, float c, float *d, float *e)
{
    *d=(a+b+c)/3;
    *e=*d;
}

---

when i compile it,the compiler said "error: conflicting types for 'mak'."
and when i change the data type of variables i,j,k,a,b,c from float to integer, the error message shows no more. how can be it happen? what should I do if i still want the type of variables i,j,k,a,b,c is float?

You haven't told the compiler what types the function mak receives, so when you pass &i etc, it will ASSUME that you are passing pointer to float (as i is a float). When you then define the function after main, you say the parameter is of type float (not a pointer). Which is not what the compiler expected.

--
Mats

You need to provide a function prototype or place the code for mak before main. In any case, your function's arguments are either wrong (float versus float pointers for the first three args), or you are calling the function incorrectly (using & when you don't need to for those same first three args).

[edit]Nevermind, matsp got it.[/edit]

i'm sorry, the code that i have posted before is the wrong code before las editing.
exactly the code like this

Code:

---

int main()
{
    float av,prc,i,j,k;
    scanf("%f %f %f", &i, &j, &k);
    mak(i,j,k,&av,&prc);
    printf("\n%f %f",av,prc);
    return 0;
}

mak(float a, float b, float c, float *d, float *e)
{
    *d=(a+b+c)/3;
    *e=*d;
}

---

as hk_mp5kpdw said, i swap the position of those function, it turn out like this.

Code:

---

#include <stdio.h>
#include <stdlib.h>

mak(float a, float b, float c, float *d, float *e)
{
    *d=(a+b+c)/3;
    *e=*d;
}
int main()
{
    float av,prc,i,j,k;
    scanf("%f %f %f", &i, &j, &k);
    mak(i,j,k,&av,&prc);
    printf("\n%f %f",av,prc);
    return 0;
}

---

amazingly, it works. it makes questions in my mind.
1.how can just swapping the position of functions makes it works?
2.and, what's wrong with the first code(before swapping)?why it goes error?

Swapping of the functions is no magic. your previous code(without swap) required function prototype declaration for mak because in C the rule is you've to declare the function before you define it. If you're not declaring the function just define it anywhere before it is used. In your previous case the compiler was checking for the declaration and you didn't provide it that's why it showed error. Actually the compiler assumed unknown number of int arguments and that's the reason after you changed them to int it showed no error.

I see..
so i must set the prorotype first in main().

but, how i declare the protoype if the function receives ponter?
because the last two arguments are pointers.
should i write "mak(float, float, float, float,float)"?

The prototype for a function is basically the same as the line that declares it:

Code:

---

void foo( int x );  /*prototype*/
...

void foo( int x ) /*declaration*/
{
    ... do stuff ...
}

---

The only real difference is that you don't actually have to name the variables anything in a prototype if you don't want to.


Quzah.

Quote:

---

Originally Posted by new-b

I see..
so i must set the prorotype first in main().

but, how i declare the protoype if the function receives ponter?
because the last two arguments are pointers.
should i write "mak(float, float, float, float,float)"?

---

For pointers declaration is like this.

int func(int *,float *,int);//the first two arguments are poniters to int and float respectively

i declare the function in the same form as BEN10 said, and it works.

thank you very much for your help.

Or you could have listened to what I said, and you'd know WHY it works.


Quzah.

so, if i don't declare the function, the compiler will assume the type of function and arguments received by function are always integers?