假定 十進位制整數 >= 0;

#include <stdio.h>

char * dto2(int x, char *s){

int y,i=0,L;

y=x;

while(1){

s[i]= y%2 + "0";

y=y/2;

i++;

if (y==0) break;

}

s[i]="\0";

L=strlen(s);

for (i=0;i<L/2; i++){y=s[i];s[i]=s[L-1-i];s[L-1-i]=y;}

return s;

}

int main()

{

int x;

char s[50];

printf("input positive int x:\n");

scanf("%d",&x);

if (x<0) {printf("x must be >=0\n"); return 1; };

dto2(x, s);

printf("%s",s );

return 0;

}