Endless C loop for input

Question

This is the code I've worked on until now, when inputting large decimals, eg 8347.93, loop begins, any assistance to resolve this problem would be appreciated

#include <stdio.h>

int main(void) {

while (1) {

int client_id;

double bal;

char type, choice1;

double amount;

double deposit = 0;

double withdraw = 0;

printf("Enter the Client ID\n");

scanf("%d", &client_id);

printf("Enter the balance\n");

scanf("%lf", &bal);

while (1) {

printf("Enter the type of transaction\n'D' for deposit\n'W' for withdraw\n");

scanf("%c", &type);

if ((type == 'W') || (type == 'w')) {

printf("Enter the amount to withdraw: \n");

scanf("%lf", &amount);

withdraw = withdraw + amount;

bal = bal - amount;

}

else if ((type == 'D') || (type == 'd')) {

printf("Enter the amount to deposit: \n");

scanf("%lf", &amount);

deposit = deposit + amount;

bal = bal + amount;

}

else {

printf("Invalid input");

continue;

}

printf("If you want to do another transaction click 'Y'/'y' \n");

printf("If you want to exit, click 'N'/'n' \n");

scanf("%c", &choice1);

if ((choice1 == 'Y') || (choice1 == 'y')) {

continue;

}

else if ((choice1 == 'N') || (choice1 == 'n')) {

break;

}

else {

printf("Invalid Input");

}

}

printf("Total Amount Deposited = %lf\n", deposit);

printf("Total Amount Withdrawn = %lf\n", withdraw);

printf("Final Balance = %lf\n", bal);

printf("Client ID = %d\n", client_id);

//break;

}

return 0;

}

Answer 1

Hey there, seems like you ran into a bit of a weird issue from C.

The %c specifier will automatically consume the leading newline characters previously in the input stream. In this case, if you pressed the enter/return key after answering the "Enter the balance:" prompt, it will consume the newline character created by that and store it into type.

In case you were curious about it, you can test this theory like this:

#include <assert.h>

// ... other code here ...

scanf("%c", &type);

// This assert will cause the program to panic!

assert(type != '\n');

A quick solution to your code would be:

scanf(" %c", &type);

If you want to standardize the solution in a way, you could do something like this:

int scanf_consume_newline(const char *format, ...) {

// Pass variadic arguments onto vfscanf

va_list argp;

va_start(argp, format);

int result = vfscanf(stdin, format, argp);

char c;

va_end(argp);

// Consume everything until newline

while ((c = getchar()) != '\n' && c != EOF) {

}

return result;

}