“”"
思路:1.a * b = a + a + a + …
　　 2.a * b = n個a相加,只需求證b = n即可
　　 3.用for 循環遍歷即可,b就是range的最大次數
　　 4.需考慮a,b有五種情況存在,但結果會有三種,正數,0,負數
“”"

def multiplication(a,b):
if a > 0 and b > 0:
sum = 0
for i in range(b):
sum += a
print(sum)
elif a < 0 and b < 0:
sum = 0
for i in range(-b):
sum += a
sum = -sum
print(sum)
elif a > 0 and b < 0:
sum = 0
for i in range(-b):
sum += a
print(-sum)
elif a < 0 and b > 0:
sum = 0
for i in range(b):
sum += a
print(sum)
else:
sum = 0
print(sum)
multiplication(8,5) #輸出結果40
multiplication(-8,-5) #輸出結果40
multiplication(8,-5) #輸出結果-40
multiplication(-8,5) #輸出結果-40
multiplication(0,-5) #輸出結果0
multiplication(8,0) #輸出結果0