Warning: X may be used uninitialized in this function

c warnings

one has not been assigned so points to an unpredictable location. You should either place it on the stack:

Vector one;one.a = 12;one.b = 13;one.c = -11

or dynamically allocate memory for it:

Vector* one = malloc(sizeof(*one))one->a = 12;one->b = 13;one->c = -11free(one);

Note the use of free in this case. In general, you'll need exactly one call to free for each call made to malloc.

c warnings

You get the warning because you did not assign a value to one, which is a pointer. This is undefined behavior.

You should declare it like this:

Vector* one = malloc(sizeof(Vector));

or like this:

Vector one;

in which case you need to replace -> operator with . like this:

one.a = 12;one.b = 13;one.c = -11;

Finally, in C99 and later you can use designated initializers:

Vector one = {   .a = 12,  .b = 13,  .c = -11};

c warnings

When you use Vector *one you are merely creating a pointer to the structure but there is no memory allocated to it.

Simply use one = (Vector *)malloc(sizeof(Vector)); to declare memory and instantiate it.

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