#include<stdio.h>
void main()
{
int x,y,z;
printf("input x,y,z:\n");
scanf("%d,%d,%d",&x,&y,&z);
printf("v=%ld\n");
}
int v(int x,int y,int z)
{
return(x*y*z);
}

#include<stdio.h>
int v(int x,int y,int z)
{
return(x*y*z);}
void main()
{int x,y,z;printf("input x,y,z:\n");
scanf("%d,%d,%d",&x,&y,&z);
printf("v=%ld\n",v(x,y,z));}

或者
#include<stdio.h>
void main()
{int v(int x,int y,int z);
int x,y,z;printf("input x,y,z:\n");
scanf("%d,%d,%d",&x,&y,&z);
printf("v=%ld\n",v(x,y,z));}
int v(int x,int y,int z)
{return(x*y*z);}