Question

int main(){
unsigned int fstNumb = 0, sndNumb = 0;
cout << "Choose the first number: ";
cin >> fstNumb;
cout << "\nChoose the second number: ";
cin >> sndNumb;
cout << "\nNow click \'m\' to multiply, \'a\' to add or \'d\' to divide: ";
char option = '\0';
cin >> option; cout << "\n\n";
float result;
if (option == 'm'){
    result = fstNumb * sndNumb;
    cout << result;
} 
else if (option == 'a'){
    result = fstNumb + sndNumb;
    cout << result;
}
else if (option == 'd') {
    if (fstNumb || sndNumb == 0)
        cout << "Cannot divide with 0 :/";
    else {
        cout << "You want the " << fstNumb << " or " << sndNumb << " to be divided?\n";
        cout << "Press 1 for " << fstNumb << " or 2 for " << sndNumb;
        char option2 = '\0';
        cin >> option2;
        if (option2 == 1){
            cout << "\nYou chose " << fstNumb;
            cout << "\nWanna divide it by how much?: ";
            unsigned short division;
            cin >> division;
            if (division == 0){
                cout << "\nCannot divide by 0!";
            }
            else{
                result = fstNumb / division;
            }
        }
        else if (option2 == 2){
            cout << "\nYou chose " << sndNumb;
            cout << "\nWanna divide it by how much?: ";
            unsigned short division;
            cin >> division;
            result = sndNumb / division;
        }
        else
            cout << "You must choose one of those 2 numbers!\n";
    }
}
else
    cout << "That's none of the letters I asked you.\n";

}

即使(fstNumb || sndNumb == 0)没有一个整数，如果0始终显示，那么问题是什么？
请注意，我没有使用布尔变量，但我认为这不应该是一个问题。

Answer 1

if (fstNumb || sndNumb == 0)与if (fstNumb == 0 || sndNumb == 0)

不同

Answer 2

if (fstNumb || sndNumb == 0)

与

相同

if (fstNumb != 0 || sndNumb == 0)

将此部分更改为（如果您不希望答案为0），

if (fstNumb == 0 || sndNumb == 0)

但如果得到0作为答案没有问题，

if ( sndNumb == 0)

Answer 3

简答：您的逻辑错误。 if (fstNumb || sndNumb == 0)与if ( (fstNumb != 0) || (sndNumb == 0) )相同，但您需要if (fstNumb == 0 || sndNumb == 0)。将其更改为后者，它将按预期工作。

解释为什么"Cannot divide with 0 :/"显示，即使fstNumb和sndNumb都不是0：

如果fstNumb非零，那么当被视为布尔值时，它的计算结果为真（零为假;其他一切都为真）。 ||的优先级低于==，因此整个表达式的计算结果为fstNumb || (sndNumb == 0)。当fstNumb != 0时，该表达式与true || (sndNumb == 0)相同，始终为真。

Answer 4

将条件if (fstNumb || sndNumb == 0)更改为if (sndNumb == 0)
因为第一个数字可以是0。

Input  : 0 12 
Answer : 0

if / else / else if语句有什么问题？

4 个答案: