3.

#include<stdio.h>
int main()
{
    int n,first,last,sum;
    printf("Enter A number:");
    scanf("%d",&n);
    last=n%10;

    while(n>=10)
    {
        n=n/10;
    }
    first=n;
    sum=first+last;
    printf("Sum Of First Digit And Second Digit = %d\n",sum);

    return 0;
}