C function float argument takes different value inside the function -

i sure i'm missing obvious here can't figure out is. in my repository, have file called ddpoly_2.c contains function called "ddpoly2". call function main function in tst5.c. if @ code in tst5_2.c, assigning x value of 2, printing , passing "ddpoly2" third argument (which per calling pattern should far can tell). print x within function "ddpoly2". see following:

x outside: 2.000000 x inside : 0.000000 nc: 2 nd: 3 

you can see x 2.000000 before function called became 0.0000000 once inside function. must missing overtly obvious here can't figure out is.

p.s. compile code using makefile in same directory.

edit: including relevant parts of code here.

calling function in tst5_2.c:

int main(int argc, char *argv[]) { //used determine section gets results printed.      float c[] = {1,1,1,0,0};     int nc = 2;     float x = 2.0;     float pd[] = {0,0,0,0,0};     int nd = 3;     printf("x outside: %f\n",x);     ddpoly2(c,nc,x,pd,nd);       } 

printing inside function ddpoly2:

#include <stdio.h>  void ddpoly2(float c[], int nc, float x, float pd[], int nd) {     int nnd, j, i;     float cnst = 1.0;     printf("x inside : %f\n",x);     printf("nc: %d\n",nc);     printf("nd: %d\n",nd); } 

you're calling function without prototype. illegal since 1999 compiler helpful , allows compatibility old c standards.

the c standard says:

if expression denotes called function has type not include prototype, integer promotions performed on each argument, , arguments have type float promoted double.

the correct solution to:

1. always have correct function prototypes.
2. always enable warnings in compilation , treat them errors.