How to convert integer to string in C?

I tried this example:

/* itoa example */
#include <stdio.h>
#include <stdlib.h>

int main ()
{
    int i;
    char buffer [33];
    printf ("Enter a number: ");
    scanf ("%d",&i);
    itoa (i,buffer,10);
    printf ("decimal: %s\n",buffer);
    itoa (i,buffer,16);
    printf ("hexadecimal: %s\n",buffer);
    itoa (i,buffer,2);
    printf ("binary: %s\n",buffer);
    return 0;
}

but the example there doesn't work (it says the function itoa doesn't exist).

Use sprintf():

int someInt = 368;
char str[12];
sprintf(str, "%d", someInt);

All numbers that are representable by int will fit in a 12-char-array without overflow, unless your compiler is somehow using more than 32-bits for int. When using numbers with greater bitsize, e.g. long with most 64-bit compilers, you need to increase the array size—at least 21 characters for 64-bit types.

Making your own itoa is also easy, try this :

char* itoa(int i, char b[]){
	char const digit[] = "0123456789";
	char* p = b;
	if(i<0){
		*p++ = '-';
		i *= -1;
	}
	int shifter = i;
	do{ //Move to where representation ends
		++p;
		shifter = shifter/10;
	}while(shifter);
	*p = '\0';
	do{ //Move back, inserting digits as u go
		*--p = digit[i%10];
		i = i/10;
	}while(i);
	return b;
}

or use the standard sprintf() function.

That's because itoa isn't a standard function. Try snprintf instead.

char str[LEN];
snprintf(str, LEN, "%d", 42);