error: incompatible types in assignment

Question

My C code

#include <stdio.h>
#include <stdlib.h>
#include "help.h"

int test(int x, P *ut) {
    int point = 10;

    ut->dt[10].max_x = NULL;
}

int main(int argc, char** argv) {

    return (EXIT_SUCCESS);
}

my help.h file code

typedef struct{
    double max_x;
    double max_y;
}X;

typedef struct{
    X dt[10];
}P;

I got an error i.e

error: incompatible types in assignment

error comes in here

ut->dt[10].max_x = NULL;

can anybody help me. thanks in advance.

Answer 1

You are trying to set a double value to NULL, which even if compiles, is mixing two incompatible terms. (In some versions of the C class library NULL is defined simply as 0, in others as (void*)0 - in latter case you get an error for such code.)

Moreover, you try to access index 10 of an array of size 10, which is out of bounds - the elements are indexed from 0 to 9. So try this:

ut->dt[9].max_x = 0.0;

Answer 2

I can see two problems in

ut->dt[10].max_x = NULL;

• The index 10 is not valid, it should be 0-9
• You are assigning a NULL value to a double. I guess you meant 0.0.

Answer 3

1. max_x is of type double, NULL is of type (void *). What makes you think they are compatible?

   Try ut->dt[10].max_x = 0.0;

2. Accessing dt[10] is out of bounds, array indexing starts at 0!