Fibonacci in C

This code calculates the Fibonacci of a number inputted by user. Calculation is done with recursion and not.
Fibonacci is declared as followed:

   fibonacci(n) = fibonacci(n-1) + fibonacci(n-2)    n>=2
   fibonacci(0) = 0
   fibonacci(1) = 1

Here is the source code of Fibonacci in C:

#include <stdio.h>

int fibonacci(int y){
    if (y==0) return 0;
    if (y==1) return 1;
    return( fibonacci(y-1)+fibonacci(y-2) );
}    

int fibonacci2(int a) {
    if (a==0) return 0;
    if (a==1) return 1;
    
    int x,y,z,i;
    for (i=1,x=0,y=0,z=1;i<a;i++) {
        x=y+z;
        y=z;
        z=x;
    }
    return(x);
}    
int main() {
    int x;
    printf("Give an integer ");
    scanf("%d",&x);
    printf("Fibonacci  of %d is %d ",x,fibonacci(x));
    printf("\nFibonacci2 of %d is %d ",x,fibonacci2(x));
    exit (0);
}

Example of output:

Give an integer: 30
Fibonacci  of 30 is 832040
Fibonacci2 of 30 is 832040