Pow c ошибки

There is no way to use the ^ (Bitwise XOR) operator to calculate the power of a number.
Therefore, in order to calculate the power of a number we have two options, either we use a while loop or the pow() function.

1. Using a while loop.

#include <stdio.h>

int main() {

    int base, expo;
    long long result = 1;

    printf("Enter a base no.: ");
    scanf("%d", &base);

    printf("Enter an exponent: ");
    scanf("%d", &expo);

    while (expo != 0) {
        result *= base;
        --expo;
    }

    printf("Answer = %lld", result);
    return 0;
}    
             

2. Using the pow() function

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

int main() {

    double base, exp, result;

    printf("Enter a base number: ");
    scanf("%lf", &base);

    printf("Enter an exponent: ");
    scanf("%lf", &exp);

    // calculate the power of our input numbers
    result = pow(base, exp);

    printf("%.1lf^%.1lf = %.2lf", base, exp, result);

    return 0;
}
     

Undefined reference to ‘pow’ error is common to occur when writing code in C or C++. The pow function in C/C++ is useful for returning the power of a given number.

To make your time valuable, we duplicated the codes in which error occurs commonly. In this post, you will learn what causes the error and how to fix it.

Why Am I Getting Indefined Reference to Pow’ Error?

The reason you are getting the undefined reference to pow’ makefile error is that your program is unable to find the definition of pow(). Moreover, it happens when your compiler is unable to locate the necessary header file that defines the pow() function.

That said, there are various causes that may trigger the undefined reference to ‘pow’ cmake error. This problem is inevitable even if you declare the math.h in your program on Linux. Although doing so declares math.h, it does not define pow. As a result, the compiler will throw the error since it is unable to find the definition.

The main reason pow() is not working in your C program is that you forgot to include the math library. Also, the reason could be, by default, the math library is not connected to your binary. Keep reading to find out how you can deal with this error even in a Linux environment.

Below is a quick breakdown of the causes of the undefined reference to function in C error.

As pointed out, you will trigger the undefined reference to ‘sqrt’ if your program does not import the math.h header file while you use the pow() function in C. Pow in C is part of the math.h header file. Therefore, if you forget to include the header file you will trigger this error or one of its variation such as undefined reference to ‘main’.

Suppose you wish to compute 9 to the power of 10 in C but you forget to include the math.h header file, then your code would look as follows:

Running this code will generate the error in question.

– Failure To Pass Argument (-lm) When Compiling

The second most common cause of the error takes place when compiling your code. As you compile your program, the failure to pass the argument (-lm) will result in the “undefined reference to pow” issue.

There could be several reasons that explain why you can’t pass an argument (-lm) which we have discussed below.

You can solve the undefined reference error by following the right syntax and importing the <math.h> header file. There could be other small reasons like not passing the required argument while compiling the program in C, C++, or Linux.

By following the same methods listed below, you can also tackle with variations of error like undefined reference to max.

– Following The Right Syntax

In C/C++ pow is a predefined function within the math.h header file. The function is useful for calculating the power of a certain number. For example, 7^4 in programming will be an expression that raises 7 to the 4th power.

This is where pow() comes in C. To be in a position to use the function, make sure you include the math.h header file.

The syntax for the ‘pow’ function takes the following form:

int pow( int base_number, int power_int)

Where the base_number is the input number you want to calculate its power with power_number indicating the power for the input value.

The function provides an easy way of finding the power of a number. Although you can write a function to calculate the power of a number, there is no need to do this since pow() already exists.

Suppose you want to calculate the square of 144 in C. You can accomplish this as follows:

Notice that you are printing the output of pow(144,2). Also, it is worth pointing out that math.h has been imported at the top of the program. So, if you run the program, the output will be 20736.

As you use the pow() in your program, make sure you import the <math.h> header file. To add it to your program in C, you should use the “#include” tag. It should look as follows:

Now, suppose you still want to calculate the value of a number a user enters raised to the power of their choosing.

To do this, you need to include the math header file. In this case, to accomplish this you need a program that looks as follows:

The output, in this case, will depend on the input from the user.

– When Compiling Pass the (-lm) Argument

As you compile your program in C, make sure you follow the right syntax, especially when using the pow(). Keep this in mind, especially when doing this on Linux. Remember to add the (-lm) argument to ensure your code connects to “libm.a” (maths library). Here is how you can write the command to pass (lm) argument and successfully compile your program.

On Linux, when you include the math.h header in the program then you are adding the pow() function declaration and not its definition. The libm.a library file holds the detailed definition for the function. A library is a collection of various object files.

The path to libm.a file on Linux is ‘/usr/lib/libm.a’. Therefore, you must pass this path to the library location with the argument as you compile your program on the terminal. Therefore, you have to link your C program with the library to make sure calls to functions such as pow() are solved. You can pass the path to the library in two ways.

First, you can provide the full path to the library file as follows:

$ gcc -o ExampleProgram ExampleProgram.c /usr/lib/libm.a

Alternatively, you can directly use -lm in the arguments. This will automatically locate the location of the math library. This is the recommended approach to linking library files using arguments. Here is how you can pass the -lm argument.

$ gcc -o ExampleProgram ExampleProgram.c -lm

FAQs

– What Is an Undefined Reference in C Programming Language?

A reference remains undefined in C programming language when a reference to a relocatable object (function, class, variable, etc) does find its definition even after searching all the object files. Also, when you use a shared object to build a dynamic application but you leave an unresolved reference definition.

– What Types of Data Does Pow() Return?

The pow() function will return the base value to the exponent. Both the base value and the power or exponent are in decimal values. This is because the pow() function accepts float, double, and int. It is important to note that function does not always work with integers.

Conclusion

In C, you will trigger this pow() error for various reasons. Here is a recap of what you learned in this post:

• The error from failure to import the math.h header file
• Another cause of the error when using pow() is no passing (lm) when compiling
• One solution to the issue is to import <math.h> header file in your program
• If running your program on Linux, compile it using GCC which has the lm argument

With this knowledge, you now easily tackle this error whenever it occurs.

C program undefined reference to pow error

Why this undefined reference to pow error raised in compilation?

When we use the pow function or any other math functions from math header in c program on linux environment (RHEL, Fedora or CentOS), need to use -lm option for compilation.

otherwise you will get undefined reference to pow error, when you compile below program with no -lm option.

#include<stdio.h>                                                              
#include<math.h>                                                                
                                                                                
float PMT (int interest, int loan_amount, int total_months) {                   
 float rate, denominator;                                                       
 rate = (float) interest/100/12;                                                
 denominator = pow((1+rate), total_months)-1;                                   
 return (rate+(rate/denominator))*loan_amount;                                  
}                                                                               
void main()                                                                     
{                                                                               
 int loan_amount, loan_term_years, num_of_emi_per_year;                         
 float rate_of_interest, pmt_value;                                             
                                                                                
 printf("nEnter loan amount: ");                                               
 scanf("%d", &loan_amount);                                                     
                                                                                
 printf("nEnter loan tearm in years: ");                                       
 scanf("%d", &loan_term_years);                                                 
                                                                                
 printf("nEnter number of EMI per year: ");                                    
 scanf("%d", &num_of_emi_per_year);                                             
                                                                                
 printf("nEnter rate of interest: ");                                          
 scanf("%f", &rate_of_interest);                                                
 pmt_value= PMT(rate_of_interest, loan_amount, loan_term_years*num_of_emi_per_year);
 printf("nEMI: %f", pmt_value);                                                
}    

Output:

$ cc emi_calculator.c
/tmp/cc4v5U2R.o: In function `PMT':
emi_calculator.c:(.text+0x5a): undefined reference to `pow'
collect2: error: ld returned 1 exit status

To fix this issue, need to use -lm option in compilation command.

Output:

$ cc emi_calculator.c -lm
$ ./a.out 

Enter loan amount: 396000

Enter loan tearm in years: 4

Enter number of EMI per year: 12

Enter rate of interest: 15

EMI: 11020.946289

C program provides expected output when running a.out file once you compiled the program with -lm option.

If you want different name instead of a.out file, we need to use -o option to create executable file with custom name.

$ cc -o emi emi_calculator.c -lm
$ ./emi
Enter loan amount: 396000

Enter loan tearm in years: 4

Enter number of EMI per year: 12

Enter rate of interest: 15

EMI: 11020.946289