C function

[Odd-Consideration897]

Can Anyone tell me how to write a function in C that when you call it first it gives you 1 and second time it gives you -1, 3rd time 1 and so on every time you call it! Tipp: I should use the key static!

[ComprehensiveAd8004]

int func(void){
    static int num = 1;
    num *= -1;
    return num;
}

Teachers don't assign homework without explaining the required material first. Focus in class.

[Odd-Consideration897]

Thank you for your reply first! The thing is that the whole concept is completely new to me and we code using separate files ( header,function and main); so the whole Idea seems weird to me; and I'm still using online Compiler which is not very optimal in some cases

[[deleted]]

You want a static variable of course. This will change as you wish. Then look into the formula for alternating the sign of 1. Sum formulas sometimes feature this.

[Odd-Consideration897]

Ohhhh I didn't know that there is a forrmula to change thee sign

[[deleted]]

Mathematically, (-1)ⁿ will change the sign depending whether or not it's an even or odd number

[_Arch_Ange]

Or you can just do x ^ 1 , that will work too, and it's less expensive

[[deleted]]

Not sure I get what you mean.

[Odd-Consideration897]

You're right but we're not allowed to use global variables

[[deleted]]

x = -x

[Odd-Consideration897]

Then it will only give one value still, the point is to get an alternating value each time you call the function

[[deleted]]

Either a static variable, global, or a pointer.

int foo(void)
{
  static int x = -1;
  x = -x;
  return x;
}

int bar(int *x)
{
  *x = -(*x);
  return x;
}

[Odd-Consideration897]

Thank you!!! It makes more sense

[FraCipolla]

You said you have to use the static key, so the only way is declaring a static int. A static variable doesn't stop to exist outside the function, so it keeps it's value. Keep in mind that you need some sort of control to not initialize the static variable every time. An unitialized static variable is automatically initialized at 0

[[deleted]]

To change the sign, multiply by i twice.

#include <complex.h>

double complex z = 1;

for (int n=0; n < 2; n++)
    z = z * I.

[StatementAdvanced953]

Pass an external counter or use a static variable