How would I get this code to be executed without using stdlib.h - c

Question

I keep receiving an error regarding malloc and I'm trying to find out how to get this code to work without using stdlib.h in the header. Just stdio.h, is this possible and how? As I'm totally confused
#include <stdio.h>
void allocate(int* score_array, const int input)
{
int iter;
for(iter = 1;iter <= 11;++iter)
{
if( (input < iter*10) && (input >= (iter-1)*10 ) )
{
++(score_array[iter-1]);
}
}
}
void printf_star(const int len)
{
int iter;
for(iter = 0;iter < len;++iter)
{
printf("*");
}
printf("\n");
}
int main()
{
int iter, size, temp;
int* buffer;
int score_array[11];
for(iter = 0;iter < 11;++iter)
{
score_array[iter] = 0;
}
printf("How many grades will you be entering?\n");
printf("Enter a number between 1 and 100: ");
scanf("%d", &size);
buffer = (int*)malloc(size*sizeof(int));
for(iter = 1;iter <= size;++iter )
{
printf("Getting grade %d. You have %d grade(s) left to enter\n", iter, size-iter+1);
printf("Enter a number between 0 and 100: ");
scanf("%d",&temp);
if( (temp>=0) && (temp <= 100) )
{
buffer[iter-1] = temp;
}
else
{
do
{
printf("Invalid Value!\n");
printf("Getting grade %d. You have %d grade(s) left to enter\n", iter, size-iter+1);
printf("Enter a number between 0 and 100: ");
scanf("%d",&temp);
}
while( (temp < 0) || (temp > 100) );
}
}
for(iter = 1;iter <= size;++iter)
{
allocate(score_array, buffer[iter-1]);
}
for(iter = 0;iter < 11;++iter)
{
printf_star(score_array[iter]);
}
return 0;
}
I keep getting this error:
hw08.c: In function ‘main’:
hw08.c:56: warning: incompatible implicit declaration of built-in function ‘malloc’

Answer 1

This is only a warning, not an actual error, so the program still compiles.
To eliminate the warning you can declare the malloc in your file:
#include <stdio.h>
extern void * malloc(unsigned long);
You could also just include stdlib.h, unless you have a major reason not to.

Answer 2

Header files just define the functions prototypes by using the extern keyword. The actual implementation of malloc resides in libc depending on the OS.
Not defining a function/system call prototype is indeed a warning, not a compile-time error, contrary to what many have conveyed in the comments!
Coming to the actual workaround, if you want to avoid using the #include <stdlib.h>, you either need to use:
#include <malloc.h> (deprecated since c89)
Define the header all by yourself, with extern void * malloc(size_t);
Credits to #Chris Rouffer too! :)

Answer 3

You need to include stdlib.h if you want to access the malloc() function, because that is where it is defined. Otherwise the compiler doesn't know what to do.
You really are supposed to include the header in your code if you want to use the function, however, in theory you could just paste the implementation of malloc() in your source and then use it from there without the header. This is a bad idea however, since anybody looking at the code would expect malloc() to refer to the standard implementation defined in stdlib.h.