C语言程序编译后正确，但是运行时总有一个 错误是怎么回事啊，，很急啊，，各位帮帮忙

#include#includeint demo(int a,int b){ if(a%b != 0) demo(b,a%b); else return b;}void main(){ int a,b; printf("input a,b:"); scanf("%d %d",&a,&b); printf("Common demo of a,b is %d\n",demo(a,b)); getch();}