Recursive positive digits sum program-CodePudding

I'm facing an issue, the program almost works correctly except it gives 1 in output result. For example num input is 123 = 1 2 3=6, instead it gives 7 as output.

I can simply fix this problem by adding -1 in the printf statement, but I want to know why this is happening.

#include<stdio.h>
int Sumdigits(int num);

int Sumdigits(int num){
    if(num<1){
        return 1;
    }
    else return (num Sumdigits(num/10));
}

int main(){
    int num;
    printf("Enter Number: ");
    scanf("%d",&num);
    printf("%d",Sumdigits(num));
}

CodePudding user response：

The problem is that Sumdigits( 0 ) will return 1 instead of 0, which does not make sense. To fix this, change

if(num<1){
    return 1;
}

to:

if(num<1){
    return 0;
}

It is also worth noting that your code will not work with negative numbers. Therefore, you may want to change the function Sumdigits to the following:

int Sumdigits( int num )
{
    if( num == 0 )
        return 0;

    if ( num < 0 )
        num = -num;

    return num % 10   Sumdigits(num/10);
}

CodePudding user response：

You are adding 1 in this if statement

if(num<1){
    return 1;

The function should be declared and defined like

unsigned int Sumdigits( unsigned int num )
{
    return num == 0 ? 0 : num % 10   Sumdigits( num / 10 );
}

If the user is allowed to deal with negative integer values then the function can be defined the following way

unsigned int Sumdigits( int num )
{
    unsigned int digit = num < 0 ? -( num % 10 ) : num % 10;

    return num == 0 ? 0 : digit   Sumdigits( num / 10 );
}