CODEWITHSUNDEEP
cfunctionvector
Federico Gentile
Federico Gentile

Reputation: 5940

How to pass vectors to a function in C

I wrote a simple C program because I just got started learning how to program. Here is the main.c file:

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>

float mul(float r[],float o[]){
  o[0] = r[0]*11;
  o[1] = r[1]*22;
  o[2] = r[2]*33;
}
//==============================================================
int main(void){
float r[3];
r[0]=1;r[1]=2;r[2]=3;
float o[3];

o=mul(r,o);

return 0;
}`

My goal is to fill vector o by using the function mul; I am required to keep the definition of the variables as it is; the only thing that I am supposed to modify is the function. When I run it by typing gcc main.c I get an error message like this:

error: incompatible types when assigning to type ‘float[3]’ from type ‘float’
o=mul(r,o);

And I have no Idea how to fix it. What am I supposed to change in my little code? as far as I learned I should pass to the function the pointers referred to the vectors but it should be the same thing of what I have done since the vector name is the pointer to the vector itself.

Thanks for your help

Upvotes: 0

Views: 273

Answers (2)

Lee Daniel Crocker
Lee Daniel Crocker

Reputation: 13171

o=mul(r,o);

assigns o to the return value of the mul function. But mul has no return value--it has no return statement at all, nor does it need one, because it operates directly on the arrays passed to it. Instead, just declare it void:

void mul(float r[], float o[]) {
    . . .

Then call it without the assignment:

mul(r, o);

Upvotes: 0

Carl Norum
Carl Norum

Reputation: 225032

  1. In C it's called an "array", not a "vector".

  2. You can't assign a value to an array.

  3. You have mul declared as returning a float, but it doesn't return anything - change that to void.

  4. When you call mul, since it doesn't return anything, you don't need the o=. Just mul(r,o), will be fine.

  5. An array is not a pointer. That said, an array does decay into a pointer to its first element in most contexts, including the function call you're using it in. Likewise, the float r[], float o[] in your mul function signature is just syntactic sugar for float *r, float *o.

Upvotes: 2

Related Questions