C程序初级题，链接错误...求助

题目是 编写一函数gcd 求两个正整数的最大公约数

我编写的程序如下
#include
#include "zylib.h"
int gcd(int x,int y );

int main()
{
int a,b,c;
printf("The program gets two positive nunbers and prints the greatest common divisor of them.\n");
printf("The first number:");
a=GetIntegerFromKeyboard();
printf("The second number:");
b=GetIntegerFromKeyboard();
c=gcd(a,b );
printf("The greatest common divisor is %d.\n",c);
return 0;
}

int gcb(int x,int y )
{
int result;
result=x if(x%result!=0||y%result!=0)
result--;
return result;
}

5作业三.obj : error LNK2001: unresolved external symbol _gcd
Debug/5作业三.exe : fatal error LNK1120: 1 unresolved externals
执行 link.exe 时出错.
这是链接时出现的错误提示...
请大家帮帮忙啊 看看是怎么回事 ？？

函数申明为gcd
函数体定义却为gcb