Thread: Newbie Help. I can't use pow and call the math library.

I am writing a calculator program. I am new to C. I am having problem with the expontential function. This program adds, subtracts, etc. I have left off some of the code but I think you get the idea.

Code:

 # include <stdio.h>
  7 
  8 double power(double int1, int int2);
  9 
 10 int main ( void )
 11 
 12 {
 13 float int1, int2, result, menu;
 14 

 else if (menu == 5)
 55 {
 56 
 57  result = power(double int1, int int2);
 58 printf("%.2lf raised to the power %d = %.2lf\n", int1, int 2, power(int1,int    2));
 59 
 double power(double int1, int int2){
 79 if ( int2 == 0)
 80 return int1;
 81 else
 82 return int1 * power (int1, int2 - 1);
 83 }

line 57 is giving me

error: expected expression before âdoubleâ

line 57
error: expected expression before âdoubleâ

line 58
expected expression before âintâ

line 58

too few arguments for format

Thanks for the help in advance.

Should more of the code be posted? No responses.

Thanks

Code:

8 double power(double int1, int int2);

This is good, you are declaring your function before you use it in main(). An observation:
- The first parameter is being labeled "int1", although its type is double. A double can represent fractional numbers as well as whole numbers. Are you using that type to allow for integers larger than the int type can support? The name "int1" is irrelevant, but looks misleading.

Code:

57  result = power(double int1, int int2);

What are you trying to do here? power() takes two arguments, like you specified in the declaration above. The first is of type double and the second is of type int. So, if I have these three variables:
x which is a double,
y which is an integer, and
z whcih is a double,
I can do:

Code:

z = power(x, y);

You do not write "double" and "int" in there before the x and y. That tells you what type of variable to supply.

Code:

59 double power(double int1, int int2){
79 if ( int2 == 0)
80 return int1;
81 else
82 return int1 * power (int1, int2 - 1);
83 }

Line 80 probably isn't what you want. Say int1 = 10, int2 = 0...is 10^0 = 10?

I also thought it was worth pointing out that the standard library already defines a function called pow(). It is defined in math.h.

Hope that help you out

Don't you need to link to the math library?
And maybe #include <math.h>

Don't you think it's kind of confusing to name a float int1 and int2?

Originally Posted by sand_man

Don't you need to link to the math library?
And maybe #include <math.h>

In the thread title, he says he can't use pow() and can't link to the math library. Probably because it's a homework assignment and he is supposed to implement pow() himself.

Note, BSmith4740, that because you define your power() funtion to be recursive (which your teacher will probably love) yet return 0 if the exponent is 0, your power() will return zero for every input: Suppose you want to calculate 2^3, then you would get

Code:

power(2, 3) = 2*power(2, 2) = 2*2*power(2,1) = 2*2*2*power(2,0) = 2*2*2*0 = 0

Your variable names are indeed chosen rather poorly. I wouldn't call them "double1" and "double2" either. More something like "base" and "exponent" perhaps?

Good luck,
Sander

--
Computer Programming: An Introdution for the Scientifically Inclined

Could anyone be kind enough to do an example of an expontential function using if else statements, while statement, or for statement. I am having a hard time picturing this in my head. I got the function call figured out but I have to take the value and raise it to an expontial function a second time.

Code:

 double power(double , int int2);  (function prototype)

while(menu=2){
result = power(  int1,  int2);
}  (function call)

 double power( double int1, int int2) {
124 if ( int2 == 0)
125 return 1;
126 else
127 return int1 * power (int1, int2 - 1);
(What I do?)

I have have tried:
temp = int3 * power( int1, int2);

This gives 2 raised to the power of 2 = 4
It should read 4 raised to the power of 2 = 8
Any ideas?

Thanks

Originally Posted by BSmith4740

Could anyone be kind enough to do an example of an expontential function using if else statements, while statement, or for statement. I am having a hard time picturing this in my head. I got the function call figured out but I have to take the value and raise it to an expontial function a second time.

What does that mean? Do you mean you need to do it not recursively, or you are having trouble with your recursive function, or something else?