Trying to create an exp(x) program

Hey all. I'm experimenting with a program that is in relation to an assignment I have. All I'm trying to do is have the user input a number, and then have the program raise "e" (as in 2.71828...) to that number. I've got something, but it's not working like I need it to. I know my program doesnt include it yet, but I want to have a printf statement saying something like "exp(x) is <answer>". Can anyone see what I'm doing wrong?

Code:

---


#include <stdio.h>
#include <math.h>

int main()
{
        double x;
        double b;

        printf("Enter an exponent for base e\n");
        scanf("&#37;lf", &x);

        b = double exp(x);
        return(b);
}

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Once you take out the erroneous double in "b = double exp(x);" everything looks like it should work.

I had tried that and I get a crazy error:

Code:

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Undefined                      first referenced
 symbol                            in file
exp                                /var/tmp//ccsUdNwM.o
ld: fatal: Symbol referencing errors. No output written to a.out
collect2: ld returned 1 exit status

---

And of course, somewhere along the way you should remember that to include the math library using gcc you need to add "-lm" to the end of your compilation line.

Forgot about that. But now there's a new problem. The program just returns exactly what I input. I.e. after it asks for a number, I input 6 and it returns the number 6.

Ok I figured it out:

Code:

---

#include <stdio.h>
#include <math.h>

main()
{
        double x;
        double b;

        printf("Enter an exponent for base e\n");
        scanf("%lf", &x);

        b = exp(x);
        printf("exp(%f) is equivalent to %lf\n", x, b);
}

---

But one last thing. The final printf (example) reads something like

Code:

---

exp(2.000000) is equivalent to 7.389056

---

Is there a way to make it so that the program doesn't spit out so many decimal places? I.e. can it just say 2.00 instead of 2.0000000...?

printf uses &#37;f for doubles.

you can use the field width thing:

%1.2f

Thanks!

what do you mean by add -lm to to the end of the compilation line

-l = GCC link 'flag', m = math library. So you're linking against the math library, ie support for math.h functions.

so would it be like

gcc-lm <filename>

More like:
gcc -lm <filename>

Without the space you are invoking the (presumably non-existent) gcc-lm instead of gcc.

Whenever on a Unix compliant system and need to know how to do something with a program, the first thing to do is 'man xxx' where xxx is the program you want to use. It might be a little difficult at first as man pages are mostly technical, but the first lines in the man page contain the various syntax rules to invoke xxx.