source name: max3.C

 #include<stdio.h>

void main()
{
int a,b,c;
clrscr();

printf(" enter any three numbers:  \n ");
scanf("%d%d%d", &a, &b, &c);
if(a>b &&  a>c)
printf(" \n maximum is A number=%d ",a);
if(b>c)
printf(" \n maximum is B number=%d ",b);
else
printf(" \n maximum is C number=%d ",c);
getch();
}
output:

enter any three numbers:  100 200 150

maximum is B number=200

enter any three numbers:  1200 452 750

maximum is A number=1200

enter any three numbers:  100 -20 1500

maximum is C number=1500