C- implicit declaration of functions time, rand, printf, all of my function calls

Question

This has been eating at me all day. I'm relatively new to C, and I CANNOT get this working and I have no idea why. I have 3 files..

I also want to apologize for the spacing as this is my first time using stack overflow... but anyways, here is the code...

assignment_1.h-----------------------------------------------------------

#ifndef ASSIGNMENT_1_H
#define ASSIGNMENT_1_H

#define NULL 0

int CalculateFactorial(int input);
int CalculateFibonacci(int input);
void ReverseArray(int size, int array[]);
void ShuffleArray(int size, int array[]);

#endif

Main.c-----------------------------------------------------------------------

#include "assignment_1.h"
#include <stdio.h>
#include <stdlib.h>
#include <time.h>


int main(){

int fact = CalculateFactorial(15);
int fib = CalculateFibonacci(15);

printf("Factorial: %d\n", fact);
printf("Fib: %d\n", fib);

int array[] = {1,2,3,4,5,6};
int size = 6;

ReverseArray(size, array);
ShuffleArray(size, array);

return 0;


}/*end main*/

assignment_1.c---------------------------------------------------------------

#include "assignment_1.h"


int CalculateFactorial(int input){

if(input<=0)    return 0;


int factorial = input;
int multiplier = input;

while(multiplier > 1){
    factorial *= multiplier;
    --multiplier;
}/*end while*/

return factorial;

}/*end calcfact*/



int CalculateFibonacci(int input){

if(input<=0)    return 0;

else if(input == 1)     return 1;

return CalculateFibonnaci(input-1) + CalculateFibonacci(input-2);

}/*end calcfib*/



void ReverseArray(int size, int array[]){

int last = size-1;
int first = 0;
int temp;

while (last-first > 1){     /*stops the loop if size is even*/

temp = array[last];
array[last] = array[first];
array[first] = temp;

++first;
--last;

if(last-first == 2)     break; /*stops loop if size is odd*/

}/*end while*/

int i;
for (i = 0; i< size;++i){
    printf("%d, ",array[i]);
}
printf("\n");

}/*end reverse*/



void ShuffleArray(int size, int array[]){

srand((unsigned int)time(NULL));

int i;
for (i = 0; i < size; ++i){

    int idx = rand()%size; /*random unsigned int between 0 and the 
                        max index of the array*/

    int temp = array[i];
    array[i] = array[idx];
    array[idx] = temp;

}/*end for loop*/

for (i = 0; i< size;++i){
    printf("%d, ",array[i]);
}
printf("\n");

}/*end shuffle*/

I keep getting a ton of errors all saying warning: implicit declaration of function '']

I greatly appreciate any help...

Answer 1

Since you're compiling assignment_1.c separately to main.c (which is reasonable if you plan on using a linker to link the two together once they're compiled), you need to include these headers in that file, too ; they don't automatically carry over from one translation unit to the other.

Insert these into assignment_1.c:

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

---

I spotted an additional error, being the definition of NULL you specified in assignment_1.h; you should never define NULL yourself, as it's a standard symbol. That'd be like writing your own printf and scanf .

NULL is defined within the <stddef.h> header. Include that, too, when you want to use NULL .