c - 在 C 中使用指针的 Scanf

Question

我有一些代码，但我会缩短它以仅显示相关部分。

// Displays the list of user’s options available
//Displays the user’s selections and sets the value of the choice
void mainMenu(int *choice);

//Displays the types of account they would like to access and sets the
//value of the chosen account type
void AccountMenu(char *typeAcct);

//Prompts the user for the amount of their deposit and updates the selected account
void DepositMoney(double *currBal);

//Asks the user if they want another transaction
void Repeat(char * doAgain);

int main(){

int choice = 0;
char repeat = 'y';
double checkBal = 575.0,
saveBal = 3750.0,
credBal = 450.0;
char typeAcct;

while(repeat!='n'){

mainMenu(&choice); //get action from user
AccountMenu(&typeAcct); //get account to perform action on from user

switch (choice){
    case 1:
        switch (typeAcct){
        case 'c':
            DepositMoney(&checkBal);
            break;
        case 's':
            DepositMoney(&saveBal);
            break;
        case 'r':
            DepositMoney(&credBal);
            break;
        } //case 1
        break;
}
Repeat(&repeat);
repeat = tolower(repeat);
}
}


// Displays the list of user’s options available
//Displays the user’s selections and sets the value of the choice
void mainMenu(int *choice){
printf("Bank Program\n\n");
printf("Please enter your choice:\n");
printf("[1] Deposit\n");
printf("[2] Withdraw\n");
printf("[3] Balance Inquiry\n\n  >> ");
scanf(" %d", choice);
}

//Displays the types of account they would like to access and sets the
//value of the chosen account type
void AccountMenu(char *typeAcct){
char choice;
printf("Please enter your choice:\n");
printf("[C] Checking\n");
printf("[S] Savings\n");
printf("[R] Credit\n\n  >> ");
scanf(" %c", &choice);
*typeAcct = tolower(choice);
}

//Prompts the user for the amount of their deposit and updates the selected account
void DepositMoney(double *currBal){
printf("Depositing money.\nHow much would you like to deposit?\n\n >> ");
double amount = 0; //deposit amount
scanf(" &f", &amount);
*currBal = *currBal + amount;
}

void Repeat(char * doAgain){
printf("Would you like to perform another transaction? (y/n)\n\n >> ");
scanf(" &c", doAgain);
}

当我执行这段代码时，它基本上运行良好。例如，如果我为 mainMenu 输入“1”，为 AccountMenu 输入“c”，则 choice 和 typeAcct 确实分别设置为“1”和“c”。

问题似乎不在于循环。我已经尝试取出循环并只运行一次但它仍然不起作用。发生的事情是，在输入我想存入的金额后，变量的值没有更新，并且 mainMenu 和 AccountMenu 再次运行(即使 DepositMoney 是主函数中的最后一行代码并且没有环形)。为什么会这样？

Answer 1

1) scanf() 用法不正确

double amount = 0;
// scanf(" &f", &amount);
scanf(" %lf", &amount);

// scanf(" &c", doAgain);
scanf(" %c", doAgain);

2) 确保您的编译器警告已完全启用。这是最重要的一点，因为大多数问题都可以通过这种方式快速识别。

3) 始终检查scanf() 的返回值。顺便说一句，"%f" 中的前导空格是不需要的，因为 "%f" 无论如何都会扫描前导空白。不过很好，有 "%c"。

if (scanf("%lf", &amount) != 1) Handle_Error();

4) tolower() 取一个int。在用户输入 \x80 到 \xFF 范围内的 char 的罕见情况下，char 的转换> to int 是一个符号扩展，可能是一个负数。不幸的是，这对 tolower() 不起作用，它对 0 到 255 和 EOF 有很好的定义，但对其他负值不起作用。

// repeat = tolower(repeat);
repeat = tolower((unsigned char)  repeat);
...
// *typeAcct = tolower(choice);
*typeAcct = tolower((unsigned char) choice);