怎么搞？老是说"G"was not declared in

#include <stdio.h>
#define X 1.5
#define Y 2.0
#define Z 3.0
float work(float A,float B ,float C,float
G );
int main()
{
float A;
float B;
float C;
float G;
float rmb;
printf("欢迎使用最新版工资结算小程序！1.0vc\n");
printf("请输入您的底薪:\n");
scanf("%f",&G);
printf("请输入您的G1总时长:\n");
scanf("%f",&A);
printf("请输入您的G2总时长:\n");
scanf("%f",&B);
printf("请输入您的G3总时长:\n");
scanf("%f",&C);
rmb=work(A,B,C,G);
printf("预测您的应发工资为:\n");
printf("%.4f\n",rmb);
return 0;
}
float work(float A,float B,float C,float G);
float rmb=G+G/21.75/8*A*X+G/21.75/8*B*Y+G/21.75/8*C*Z;
printf("亲，需要努力哦！(๑>؂<๑）!\n");
printf("欢迎下次访问!\n");
return rmb;
}