Hello,  thanks for stopping in. I am fuddling through some exercises on a certain website, and I have come across a very frustrating bug I can't seem to fix.

The Problem:
Given a square matrix of size N×N, calculate the absolute difference between the sums of its diagonals.

Sample Input:
3
11 2 4
4 5 6
10 8 -12

First line is N, and the expected result of this example is 15.
If I hardcode in the value for N, this code works just peachy. It's when I am trying to actually read in the value of the first line from stdin that I am having a problem.

I seem to be unable to convert the string input to an integer to use later on. The code:

import std.stdio, std.math, std.string, std.conv;

void main(){
    auto matrix_size = readln;

    //below I have commented out the offending call to to!int and replaced it with a hardcoded value 3 in order to force it to work.
    auto ms = 3;//matrix_size.to!int;
    int[][] matrix = new int[][ms];
    for(int i = 0; i < ms; i++){
        string[] string_nums = readln.split;
        foreach (num; string_nums){
            auto value = num.to!int;
            matrix[i] ~= value;
        }
    }

    int primary_sum = 0;
    int secondary_sum = 0;
    int j = 0;
    int i = ms - 1;
    //determine diagonal sums
    for(int row = 0; row < ms; ++row){
        primary_sum += matrix[row][j];
        secondary_sum += matrix[row][i];
        ++j;
        --i;
    }
    auto result = abs(primary_sum - secondary_sum);
    result.writeln;
}

On Wednesday, 30 December 2015 at 01:36:56 UTC, Michael S wrote:
>     auto matrix_size = readln;

Change that to

auto matrix_size = readln.strip;


and you should be in business. readln() returns any leading spaces and the newline character at the end of the line too, which is why to is throwing.

The .strip function will trim that whitespace off.

On Wednesday, 30 December 2015 at 01:38:32 UTC, Adam D. Ruppe wrote:
> On Wednesday, 30 December 2015 at 01:36:56 UTC, Michael S wrote:
>>     auto matrix_size = readln;
>
> Change that to
>
> auto matrix_size = readln.strip;
>
>
> and you should be in business. readln() returns any leading spaces and the newline character at the end of the line too, which is why to is throwing.
>
> The .strip function will trim that whitespace off.

Wow thank you Adam. I didn't expect to have a reply so quickly, especially a slam dunk like that one. It works perfectly now!