The following Objective-C program prints sum of digits of a number entered by user. This program will only compile in latest compilers as it uses ARC paradigm. The program uses scanf c function to read user input.

// Print sum of digits of a user entered number
#import <foundation foundation.h>

int main(int argc, const char * argv[])
{

    @autoreleasepool {
        int number,digit,sum=0, temp;

        NSLog(@"Enter a number:");
        scanf("%i", &number);
        temp = number;
        
        while(temp > 0) {
            digit = temp%10;
            sum += digit;
            temp = temp/10;
        }
        NSLog(@"Sum of digits of %i = %i",number,sum);
        
    }
    return 0;
}