This question already has answers here:
Why do you have to link the math library in C?
(14 answers)
Closed 9 years ago.
I also entered include<math.h> but it still doesnt work. People are saying to enter -Im but im new to this where do I put -Im and how do I fix this.
#include <stdio.h>
#include <stdlib.h>
#include<math.h>
int main()
{
float a=0, b=0, c=0, root1=0, root2=0;
printf("Enter the value of a,b and c to determine the roots\n");
scanf("%f%f%f",&a,&b,&c);
root1=(-b+sqrt(b*b-4*a*c))/(2*a);
root1=(-b-sqrt(b*b-4*a*c))/(2*a);
printf("The first roots of the quadratic equation are\nFirst root=%.1f\nSecond root=%.1f",root1,root2);
return 0;
}
You have a copy-paste bug here:
root1=(-b+sqrt(b*b-4*a*c))/(2*a);
root1=(-b-sqrt(b*b-4*a*c))/(2*a);
should be:
root1=(-b+sqrt(b*b-4*a*c))/(2*a);
root2=(-b-sqrt(b*b-4*a*c))/(2*a);
Also you may need to link with the math library, e.g.
$ gcc -Wall foo.c -o foo -lm
Two things: first you copy pasted "root1" twice so you will lose the "plus" value and root2 will be zero. Second, for the benefits of others, the problem is most probably at compile time and the googled answer is there:
http://www.cs.cf.ac.uk/Dave/C/node17.html
And you should test for imaginary values:
if(b*b-4*a*c < 0){
printf("error: complex solution unsupported, see http://en.wikipedia.org/wiki/Square_root\n");
exit(1);
}
Related
Why does this compile and run this w/o the "-lm" switch on gcc:
#include <stdio.h>
#include <math.h>
int main()
{
printf("2 to the 8th power is %f\n",pow(2.0,8.0));
return(0);
}
but this:
#include <stdio.h>
#include <math.h>
int main()
{
float a,b;
a = 2.0;
b = 8.0;
printf("2 to the 8th power is %f\n",pow(a,b));
return(0);
}
gives the error:
undefined reference to `pow'
unless you link the math library with -lm
The behavior is the same if I use doubles rather than floats. Is there some sort of rudimentary pow() function hidden in standard library, or is the linker just resigned to working with idiots and links the math library for really simple cases?
I'm using gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0 if that makes any difference. It's not a big deal, just curious why that happens, thanks!
I had myself, a problem of understanding, what is wrong with the above. I got the same behaviour with gcc -O0. Running executable with strace and gdb showed that no function call made at all.
Scratched my head, read some comments and got it. Me alone, would have guessed the answer for hours. All credits goes to commenters
Try to change your code to
....
double t = (int)(2.0 + 1.0) % 2 + 1.0;
double r = pow(2.0+t,8.0);
....
With -O0 flag you should hopefully get undefined reference to 'pow' message.
This question already has answers here:
Why do you have to link the math library in C?
(14 answers)
Closed 4 years ago.
Just starting to learn C, and I found this example program on a C tutorial website, and it is giving an error upon compiling.
Here is the program, calculates the square root of a number based on user input:
#include <stdio.h>
#include <math.h>
int main()
{
double num, root;
/* Input a number from user */
printf("Enter any number to find square root: ");
scanf("%lf", &num);
/* Calculate square root of num */
root = sqrt(num);
/* Print the resultant value */
printf("Square root of %.2lf = %.2lf", num, root);
return 0;
}
I compile it using gcc in Ubuntu:
gcc -o square_root square_root.c
And here is the error:
/tmp/cc9Z3NCn.o: In function `main':
square_root.c:(.text+0x4e): undefined reference to `sqrt'
collect2: error: ld returned 1 exit status
What am I doing wrong? I can see that the math module is imported, so why the error?
Again, I just started studying C today, and I just want to figure out how to get programs to run. Thank you for your patience as it must be something obvious.
sqrt lives in the math library, so you need to tell your program to link to it with -lm:
gcc -o square_root square_root.c -lm
You need to compile it with -lm flag
gcc -o square_root square_root.c -lm
This question already has answers here:
What is an undefined reference/unresolved external symbol error and how do I fix it?
(39 answers)
Closed 6 years ago.
I hope someone can help me. I am working through CS50x and am working on Pset1 - greedy. I am getting the following error whenever I compile my code:
/tmp/greedy-46be96.o: In function `main':
greedy.c:(.text+0x95): undefined reference to `round'
clang: error: linker command failed with exit code 1 (use -v to see invocation)
Any help will be greatly appreciated. I apologise if the question is vague, I have tried to be in depth. I have used man round in the terminal, and have searched everywhere, trying different solutions, but nothing has worked.
#include <stdio.h>
#include <cs50.h>
#include <math.h>
int main(void)
{
float owed;
float change;
float quarter = 0.25;
float dime = 0.10;
float nickel = 0.05;
float penny = 0.01;
do {
printf("How much change is owed?: ");
owed = GetFloat();
} while(owed <= 0);
change = round(owed * 100);
}
I am using this command to compile my code:
clang -o greedy greedy.c -lcs50
The following should work when you compile:
clang -o greedy greedy.c -lcs50 -lm
This links the math library for the compiler.
This question already has answers here:
Undefined reference to sqrt (or other mathematical functions)
(5 answers)
Closed 5 years ago.
So I'm trying to make a program that calculates the quadratic formula, but when I try to compile the code, I get the following:"undefined reference to sqrt"
But I tried defining sqrt via math.h and 2 other times in the code.
I have attached my code
Any help would be greatly appreciated
#include <stdio.h>
#include <math.h>
#include <stdlib.h>
double sqrt(double);
int main (void) {
double sqrt(double);
int a,b,c;
double discriminant,squarerootofdis,root1, root2;
printf("Please enter the coefficient of x^2:");
scanf("%d",&a);
printf("Please enter the coefficient of x:");
scanf("%d",&b);
printf("Please enter the integer value of the ploynomial:");
scanf("%d",&c);
if (a==0 && b==0)
{printf("This case is extremely degenerate");}
else if (a==0 && b!=0)
{root1=-c/b;
printf("Degenerate one real root: %lf\n",root1);}
else{
discriminant = ((b*b)-(4*a*c));
squarerootofdis = sqrt(discriminant);
root1 = (squarerootofdis-b)/(2*a);
root2 = (-squarerootofdis-b)/(2*a);
if (discriminant>0)
printf("Two real roots: %lf\n %lf\n", root1, root2);
else if (discriminant == 0)
printf("Degenerate one real root: %lf\n",root1);
else if (discriminant<0)
printf("Two complex roots: %lf\n %lf\n", root1, root2);
}
}
To use the sqrt function (or any function defined in math.h), you'll have to link the m library:
~$ gcc -lm yourcode.c -o program
Did you compile with -lm linked?
Header file will provide the decalration to the sqrt() function. To have the definition, you need to link with the math library consisting of the function definition.
Example:
gcc test.c -o output -lm
Please use the below command
gcc test.c -lmath
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Closed 7 years ago.
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I'm completely new to programming. I'm actually learning from a Harvard class on iTunes U. When trying to code along side the instructor I've ran into a problem. I can't run my .c program in terminal. I've tried the sudo commands, and I've searched with Google and I can't seem to find an answer, probably because I'm so new to programming. It's probably something I've overlooked or I just don't understand yet.
#include <stdio.h>
int
main(void)
{
printf("temperature in f: ");
float f = GetFloat();
float c=f / 9.0 * (f-32);
Printf("%. if F = %. if c\n", f, c)
I'm using Sublime text editor on a MacBook with Mac OS X Yosemite (10.10.x).
Your compiler should have warn you about some errors:
// string.c
#include <stdio.h>
int main(void) // There must be a return statement
{
printf("temperature in f: ");
float f = GetFloat();
float c = f / 9.0 * (f-32);
printf("%f if F = %f if c\n", f, c); // Missing ';' is the most common syntax error
return 0; // Here is the return
} // Do not forget to close your brackets
When you do:
gcc string.c -o myprogram
It will tell you what is wrong in your program. Once you have fixed all the errors you can run the program with:
./myprogram
Understand that you cannot run a C-file: the .c contains human-readable instructions for the machine. You have to compile it, i.e. translate it into a language that your computer will understand : it is roughly your compiled myprogram (and you do not want to open it to look what it contains, it will burn your eyes :p).
Just adding to the below answer your compiler should throw the below error also:
undefined reference to `Printf'
check case of your printf()