How do I fix/debug a "lvalue required as left operand of assignment" error?-CodePudding

I'm very new to coding. I'm trying to make a simple math equation making use of float, using this code:

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

int car() {

int r1;
int m1;
int m2;
 
float lift_a_car(const int r1, const int m1, const int m2);

lift_a_car = r1   (2 * m1 / (m1   m2));

printf("%.4f\n", lift_a_car(2, 80, 1400));

return 0;
}

Whenever I run it, I get this error:

arrays.c:12:12: error: lvalue required as left operand of assignment
   12 | lift_a_car = r1   (2 * m1 / (m1   m2));

I couldn't find a good explanation for this error anywhere. Can someone please explain this error to me? And is there any way to simplify/improve this code overall?

CodePudding user response：

lift_a_car is a function and you cannot assign to a function in C. If you wanted to define a function, you should specify a function body using curly braces:

float lift_a_car(const int r1, const int m1, const int m2)
{
    return r1   (2 * m1 / (m1   m2));
}

Note that you cannot define a function inside of another function in C, so your lift_a_car function must be defined outside and before your car function.

CodePudding user response：

Try something like that:

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

// functions shall be defined here
float lift_a_car(int r1, int m1, int m2)
{
    // note to get a float result, you need to cast to float
    return (r1   (2 * (float)m1 / (m1   m2)));
}

int main() {
    // Here you can call the function
    printf("%.4f\n", lift_a_car(2, 80, 1400));

    return 0;
}

CodePudding user response：

It seems like you want to create a function lift_a_car. It must be outside of int car as nested functions are not supported. Functions must be top-level entities in C, not within any scope ({}). (In your code, lift_a_car is inside car). And the name of the entry-point function must be main. Since your car function returns 0, it seems like you are trying to use car instead of the name main :

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

float lift_a_car(const int r1, const int m1, const int m2)
{
    float result = r1   (2 * m1 / (m1   m2));
    return result;
}


int main() 
{

    int r1 = 2;
    int m1 = 80;
    int m2 = 1400;
 
    printf("%.4f\n", lift_a_car(r1, m1, m2));

   return 0;
}

Also, since you are performing division with two integers, the decimal points will be truncated, so cast one of the values first to float to retain the decimal points:

float lift_a_car(const int r1, const int m1, const int m2)
{
    float result = r1   ((float) 2 * m1 / (m1   m2));
    return result;
}

We could try to help more if you provide more details about what you are trying to do.