Loop:

-20°C = -4°F
-19°C = -2.2°F
-18°C = -0.4°F
-17°C = 1.4°F
-16°C = 3.2°F
-15°C = 5°F
-14°C = 6.8°F
-13°C = 8.6°F
-12°C = 10.4°F
-11°C = 12.2°F
-10°C = 14°F
-9°C = 15.8°F
-8°C = 17.6°F
-7°C = 19.4°F
-6°C = 21.2°F
-5°C = 23°F
-4°C = 24.8°F
-3°C = 26.6°F
-2°C = 28.4°F
-1°C = 30.2°F
0°C = 32°F
1°C = 33.8°F
2°C = 35.6°F
3°C = 37.4°F
4°C = 39.2°F
5°C = 41°F
6°C = 42.8°F
7°C = 44.6°F
8°C = 46.4°F
9°C = 48.2°F
10°C = 50°F
11°C = 51.8°F
12°C = 53.6°F
13°C = 55.4°F
14°C = 57.2°F
15°C = 59°F
16°C = 60.8°F
17°C = 62.6°F
18°C = 64.4°F
19°C = 66.2°F
20°C = 68°F
21°C = 69.8°F
22°C = 71.6°F
23°C = 73.4°F
24°C = 75.2°F
25°C = 77°F
26°C = 78.8°F
27°C = 80.6°F
28°C = 82.4°F
29°C = 84.2°F
30°C = 86°F
31°C = 87.8°F
32°C = 89.6°F
33°C = 91.4°F
34°C = 93.2°F
35°C = 95°F
36°C = 96.8°F
37°C = 98.6°F
38°C = 100.4°F
39°C = 102.2°F
40°C = 104°F

var_dump:

array(61) { [0]=> int(-20) [1]=> int(-19) [2]=> int(-18) [3]=> int(-17) [4]=> int(-16) [5]=> int(-15) [6]=> int(-14) [7]=> int(-13) [8]=> int(-12) [9]=> int(-11) [10]=> int(-10) [11]=> int(-9) [12]=> int(-8) [13]=> int(-7) [14]=> int(-6) [15]=> int(-5) [16]=> int(-4) [17]=> int(-3) [18]=> int(-2) [19]=> int(-1) [20]=> int(0) [21]=> int(1) [22]=> int(2) [23]=> int(3) [24]=> int(4) [25]=> int(5) [26]=> int(6) [27]=> int(7) [28]=> int(8) [29]=> int(9) [30]=> int(10) [31]=> int(11) [32]=> int(12) [33]=> int(13) [34]=> int(14) [35]=> int(15) [36]=> int(16) [37]=> int(17) [38]=> int(18) [39]=> int(19) [40]=> int(20) [41]=> int(21) [42]=> int(22) [43]=> int(23) [44]=> int(24) [45]=> int(25) [46]=> int(26) [47]=> int(27) [48]=> int(28) [49]=> int(29) [50]=> int(30) [51]=> int(31) [52]=> int(32) [53]=> int(33) [54]=> int(34) [55]=> int(35) [56]=> int(36) [57]=> int(37) [58]=> int(38) [59]=> int(39) [60]=> int(40) } array(61) { [0]=> int(-4) [1]=> float(-2.200000000000003) [2]=> float(-0.3999999999999986) [3]=> float(1.3999999999999986) [4]=> float(3.1999999999999993) [5]=> int(5) [6]=> float(6.800000000000001) [7]=> float(8.600000000000001) [8]=> float(10.399999999999999) [9]=> float(12.2) [10]=> int(14) [11]=> float(15.8) [12]=> float(17.6) [13]=> float(19.4) [14]=> float(21.2) [15]=> int(23) [16]=> float(24.8) [17]=> float(26.6) [18]=> float(28.4) [19]=> float(30.2) [20]=> int(32) [21]=> float(33.8) [22]=> float(35.6) [23]=> float(37.4) [24]=> float(39.2) [25]=> int(41) [26]=> float(42.8) [27]=> float(44.6) [28]=> float(46.4) [29]=> float(48.2) [30]=> int(50) [31]=> float(51.8) [32]=> float(53.6) [33]=> float(55.4) [34]=> float(57.2) [35]=> int(59) [36]=> float(60.8) [37]=> float(62.6) [38]=> float(64.4) [39]=> float(66.2) [40]=> int(68) [41]=> float(69.8) [42]=> float(71.6) [43]=> float(73.4) [44]=> float(75.2) [45]=> int(77) [46]=> float(78.8) [47]=> float(80.6) [48]=> float(82.4) [49]=> float(84.2) [50]=> int(86) [51]=> float(87.8) [52]=> float(89.6) [53]=> float(91.4) [54]=> float(93.2) [55]=> int(95) [56]=> float(96.8) [57]=> float(98.6) [58]=> float(100.4) [59]=> float(102.2) [60]=> int(104) }

print_r:

Array ( [0] => -20 [1] => -19 [2] => -18 [3] => -17 [4] => -16 [5] => -15 [6] => -14 [7] => -13 [8] => -12 [9] => -11 [10] => -10 [11] => -9 [12] => -8 [13] => -7 [14] => -6 [15] => -5 [16] => -4 [17] => -3 [18] => -2 [19] => -1 [20] => 0 [21] => 1 [22] => 2 [23] => 3 [24] => 4 [25] => 5 [26] => 6 [27] => 7 [28] => 8 [29] => 9 [30] => 10 [31] => 11 [32] => 12 [33] => 13 [34] => 14 [35] => 15 [36] => 16 [37] => 17 [38] => 18 [39] => 19 [40] => 20 [41] => 21 [42] => 22 [43] => 23 [44] => 24 [45] => 25 [46] => 26 [47] => 27 [48] => 28 [49] => 29 [50] => 30 [51] => 31 [52] => 32 [53] => 33 [54] => 34 [55] => 35 [56] => 36 [57] => 37 [58] => 38 [59] => 39 [60] => 40 )
Array ( [0] => -4 [1] => -2.2 [2] => -0.4 [3] => 1.4 [4] => 3.2 [5] => 5 [6] => 6.8 [7] => 8.6 [8] => 10.4 [9] => 12.2 [10] => 14 [11] => 15.8 [12] => 17.6 [13] => 19.4 [14] => 21.2 [15] => 23 [16] => 24.8 [17] => 26.6 [18] => 28.4 [19] => 30.2 [20] => 32 [21] => 33.8 [22] => 35.6 [23] => 37.4 [24] => 39.2 [25] => 41 [26] => 42.8 [27] => 44.6 [28] => 46.4 [29] => 48.2 [30] => 50 [31] => 51.8 [32] => 53.6 [33] => 55.4 [34] => 57.2 [35] => 59 [36] => 60.8 [37] => 62.6 [38] => 64.4 [39] => 66.2 [40] => 68 [41] => 69.8 [42] => 71.6 [43] => 73.4 [44] => 75.2 [45] => 77 [46] => 78.8 [47] => 80.6 [48] => 82.4 [49] => 84.2 [50] => 86 [51] => 87.8 [52] => 89.6 [53] => 91.4 [54] => 93.2 [55] => 95 [56] => 96.8 [57] => 98.6 [58] => 100.4 [59] => 102.2 [60] => 104 )