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@cocet33000

# python3の除算は型に注意 A//B != int(A/B)

``````A//B != int(A/B)
``````

# 問題点

Python3では`/`演算子を使用した場合、`float`に変換して除算が行われます。
そのため、以下のコードを実行すると問題が生じます。

``````a = 123
b = 456

A = 10**9 + 123
B = 10**9 + 456

c = a*b/2
d = a*b//2

C = A*B/2
D = A*B//2

print("a*b/2       =",c)
print("int(a*b/2)  =",int(c))
print("a*b//2      =",d)

print("A*B/2       =",C)
print("int(A*B/2)  =",int(C))
print("A*B//2      =",D)
``````

``````a*b/2       = 28044.0
int(a*b/2)  = 28044
a*b//2      = 28044
A*B/2       = 5.00000289500028e+17
int(A*B/2)  = 500000289500028032
A*B//2      = 500000289500028044
``````

# 原因

python3では`int型`は無限の桁数を持つのに対して、`float型`は有限です、そのため`/`演算子により`A*B``float型`で実行され、大きい数字の場合には以下の様な結果となってしまうのです。お気をつけあれ。

``````A = 10**9 + 123
B = 10**9 + 456

c = (A*B)
d = float(A*B)

if c != d:
print("一致しません")
print("c", c)
print("d", d)
``````

``````一致しません
c 1000000579000056088
d 1.000000579000056e+18
``````
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Help us understand the problem. What are the problem?