Mathematica- If statement not performing true/false - if-statement

Question

I have a notebook set up to run through an exhaustive search of numbers in an array used in an equation, if the equation equals a defined variable, then it returns the values of the variables in the equation. The only problem is, the If statement in the last For-loop never runs through the true/false/neither functions. The only way I've been able to get it to do anything is to use a generic Print[blah], of which it then proceeds to print absolutely every iteration through all the For-loops. Here is what I have so far-
AvTarget := -95
arr := {1, 1.1, 1.2, 1.3, 1.5, 1.6, 1.8, 2, 2.2, 2.4, 2.7, 3, 3.3,
3.6, 3.9, 4.3, 4.7, 5.1, 5.6, 6.2, 6.8, 7.5, 8.2, 9.1, 10}
trueArr := {}
falseArr := {}
For[i = 1, i <= Length[arr], i = i + 1,
For[j = 1, j <= Length[arr], j = j + 1,
For[k = 1, k <= Length[arr], k = k + 1,
If[Abs[
AvTarget - (arr[[i]] + arr[[k]] + (arr[[i]] + arr[[k]])/
arr[[j]])] < 1000, Append[trueArr, {i, j, k}],
Append[falseArr, 1], Append[falseArr, 0]]
]
]
]
Length[trueArr]
Length[falseArr]
I haven't dealt with loops in mathematica yet so I'm not sure what the issue is.
EDIT-
Ok so this code now works the way I need it to -
AvTarget = -95;
tol = 0.1;
arr := {1, 1.1, 1.2, 1.3, 1.5, 1.6, 1.8, 2, 2.2, 2.4, 2.7, 3, 3.3,
3.6, 3.9, 4.3, 4.7, 5.1, 5.6, 6.2, 6.8, 7.5, 8.2, 9.1, 10}
trueArr = {};
falseArr = {};
For[i = 1, i <= Length[arr], i++,
For[j = 1, j <= Length[arr], j++,
For[k = 1, k <= Length[arr], k++,
If[Abs[
AvTarget - (-(arr[[i]] + arr[[k]] + (arr[[i]]*arr[[k]])/
arr[[j]]))] <= tol,
trueArr = Append[trueArr, {arr[[i]], arr[[j]], arr[[k]]}],
Append[falseArr, 1], Append[falseArr, 0]]
]
]
]
Length[trueArr]
From there if Length > 0 I can just add an If to display the results. What would be the best way to have all the results within the tolerance printed in order of closest to AvTarget?

Answer 1

Loops are almost always the wrong way to go with Mathematica. I rewrote your original code to
avTarget = -95;
arr := {1, 1.1, 1.2, 1.3, 1.5, 1.6, 1.8, 2, 2.2, 2.4, 2.7, 3, 3.3,
3.6, 3.9, 4.3, 4.7, 5.1, 5.6, 6.2, 6.8, 7.5, 8.2, 9.1, 10};
triples = Tuples[arr, 3];
trueArr = Select[triples, Abs[avTarget - (#[[1]] + #[[3]] + (#[[1]] + #[[3]])/#[[2]]) <
1000] &];
falseArr = Complement[triples,trueArr];
I've been using Mathematica for about 20 years, I can't recall ever needing loops. Sure, sometimes it's easier to express an algorithm using loops than the functional alternatives that Mathematica provides but you should really kick away the crutches that they provide and walk the Mathematica way.

Answer 2

You should assign the return value of Append to the respective variable.

Answer 3

Append[trueArr, {i,j,k}] gives trueArr with {i,j,k} appended and then discards the result. You want trueArr = Append[trueArr, {i, j, k}].
Also, ":=" is the SetDelayed operator. You should be using "=".