Salut,
#include<stdio.h>

int main()
{
int nb,q,r,i,j;
int tab[20];

printf("Entrez un entier : ");
scanf("%d",&nb);

printf("%d en binaire : ",nb);
q=1;
i=0;
while( q != 0 )
{
q=nb/2;
r=nb%2;
nb=q;

tab[i++]=r;
j=i;
}

for(i=j-1;i>=0;i--)
printf("%d",tab[i]);
printf("\n");
return 0;
}