Why Do I Get Clang: Error: Linker Command Failed with Exit Code 1?

You missed the definition of function int power (int base,int n) which is given after your main ends on the next page of the book.

When you declare prototype of a function you need to define what it should do you just declared the power function and never defined that, that's why you got error.

Include the following definition, your code will compile the way you wants it to be.

int power (int base,int n){
int i,p;
p=1;
for (i=1;i<=n;++i)
p=p*base;
return p;
}

PRE-EDIT ANSWER NOW THIS IS NOT RELEVANT BUT USEFULL

I think you want to use function pow() defined in math.h.

double pow(double a, double b)

The C library function pow(double a, double b) returns a raised to the power of b. This function returns a double value so to print that correct specifier will be "%lf".

In this case you just need to include header file

#include<math.h>

In your program.

There is no need to give function declaration int power(int m, int n);

The error you are having is due to giveing I as on of the parameter to pow() because when you will compile your code (after including math.h and using pow() replacing i with any integer numbers will compile your code and will give proper output.

printf("%lf %lf %lf\n", i, pow(2,3), pow(3,2));

This will give you proper result but when you compile it with

for (i=0; i<10; ++i){
printf("%lf %lf %lf\n", i, pow(2,i), pow(-3,i));
}

It throws same error so I think pow() takes only constants as input so it won't run in for loop.

And if you don't want to include math.h you can simply declare

extern double pow (double base, double exponent); 

That will link correctly with the library code without using the math.h include file, here is an example.

int main() {
extern double pow (double base, double exponent);
printf("%lf",pow( 8.0, 8.0 ));
return 0;
} 

For more on pow() you can check man page on Linux i.e. man pow.

you can define power function

int power(int m, int n){
//implement the function body
}

then your issue will get fixed.

Your getting error, because there is not deceleration for the defined function. So add the deceleration as shown in above.

There is a standard library function which does just that...

#include <math.h>
double pow(double x, double y)

You have to link it explicitly because the default linker, that is ld invoked when no other options given, doesn't link with standard math library.

So you have to do it like...

gcc file.c -lm

First you get the error because the compiler can not find the definition of the power function that you are using. Even if you write

int power(int m, int n);

There is an error because you are not defining the function. There is missing {} at the end of the definition and even if you are putting it at the end of the definition, you will get an error because you are not returning nothing for a int function. So, at least if you want to define a function, you have to proceed like this :

int power(int m, int n){return 0};

Then, you will be able to use your function power() in the main function. But, you are doing nothing in the power() function, so you will get nothing back of calling it. If you want to compute the power of a number, you can use the function pow() that is present in the cmath library. A straightforward way of doing it is something like this :

#include <stdio.h> // printf
#include <cmath>  // pow()
#include <iostream> //cout

void main()
{
    for (int i = 0; i < 10; i++)
        std::cout << i << " " << pow(2, i) << " " << pow(-3,i) << std::endl;
}

I included the iostream to use a different way of printing out using the object cout defined in the std namespace. Note that the pow() function has some requirements for its definition, so be careful with the types you are using. You can take a look at for more details.