#include<stdio.h>
#include<math.h>
double profits(double I,double S,int Y);
void main()
{
    int Y;
    double S,I,M,n;
    printf("请输入年利润，投资钱数和年数:");
    scanf("%lf %lf %d",&I,&S,&Y);
    printf("第%d的年利润为%lf\n",Y,profits(I,S,Y));

}
double profits(double i,double j,int k)
{
    int Y;
    double I,S,n,M;
    n=pow(1+I,Y);
    M=S*n;
    return M;
}

你的这个参数是怎么传递的呢？？？真是服了呀！回去把书好好看看！！！

还没学到这里。

#include<stdio.h>
#include<math.h>
double profits(double I,double S,int Y);
void main()
{
    int Y;
    double S,I;
    printf("请输入年利润，投资钱数和年数:");
    scanf("%lf %lf %d",&I,&S,&Y);
    printf("第%d的年利润为%lf\n",Y,profits(I,S,Y));

}
double profits(double I,double S,int Y)
{
 
    double n,M;
    n=pow(1+I,Y);
    M=S*n;
    return M;
}

#include<stdio.h>
#include<math.h>
double profits(double I,double S,int Y);
void main()
{
    int Y;
    double S,I,M,n;
    printf("请输入年利润，投资钱数和年数:");
    scanf("%lf %lf %d",&I,&S,&Y);
    printf("第%d的年利润为%lf\n",Y,profits(I,S,Y));

}
double profits(double i,double j,int k)
{
    int Y;                        //你这里把主函数的Y传给了k,但是在子函数中你的Y好像没有值吧.
    double I,S,n,M;
    n=pow(1+I,Y);
    M=S*n;
    return M;
}

#include<stdio.h>
#include<math.h>
double profits(double I,double S,int Y);
void main()
{
    int Y;
    double S,I;
    printf("请输入年利润，投资钱数和年数:");
    scanf("%lf %lf %d",&I,&S,&Y);
    printf("第%d的年利润为%lf\n",Y,profits(I,S,Y));

}
double profits(double i,double j,int k)
{
    double n,M;
    n=pow(1+i,k);
    M=j*n;
    return M;
}
这样就好了吧