Could we find the largest among three numbers using 'for' and if?

I have the following program, please check it

#include<stdio.h>

main()

{

int a,b,c,sum=o,i';

printf("enter the numbers");

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

sum=a+b+c;

for(i=sum;i<=sum,i--)

{

if(i==a||i==b||i==c)

printf("%d the greatest");

exit();

}}........please clarify the logic if it is correct to the intention..