c - Function run 2 times.? -

i made program, code compiled thought program takes 5 inputs user takes 10 inputs.

#include <stdio.h> int greatest_number(); int main() {     greatest_number();     printf("greatest number %d", greatest_number());     return(0); }  int greatest_number() {     int a[6], x, i, z, y; 

i don't know why loop takes 10 inputs user
programmed take 5 inputs for(x=0; x<5; x++) { printf("enter number:"); scanf("%d", &a[x]); } a[x]=0; x=0, i=1; y=0; z=a[x]; while(a[x]) { if(z>a[i]){ z=a[y]; }else { z=a[i]; y=i; } x++; i++; } return(z); }

in code snippet function greatest_number called twice

greatest_number(); ^^^^^^^^^^^^^^^^^ printf("greatest number %d", greatest_number());                                 ^^^^^^^^^^^^^^^^^ 

the first call redundant , result discarded.

also seems entered elements have negative values (except last element has have understood sentinel value) function return sentinel value.