C program undefined reference to pow error fix

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