source file name: MaxFun.C 

int max(int m, int n) // declaration and definition

{

int res;

if(m>n)

res=m;

else

res=n;

return res;

}

void main()

{

int a,b;

int result;

clrscr();

printf("enter 2  numbers: ");

scanf("%d%d",&a,&b);

result= max(a,b);   // calling function

printf(" max value=%d ",result);

getch();

}

output:

1. enter 2 numbers:  

500 100

max value= 500

2. enter 2 numbers:  

225  160

max value= 225