Newbie Problem with cin

trs2988 · #1 08-Feb-2004, 10:57

I'm pretty new at C++, so please work with me. I'm trying to make a small program that calculates the bank interest of an online game that I manage. Here's the complete code for the program, so far:

CPP / C++ / C Code:

#include <stdio.h>
#include <iostream.h>

int main() {
string response;
int inBank;
int millions;
int interest;
int days;
int origDays;
while(1) {
cout << endl << "Type I to calculate interesting, or X to exit: ";
cin >> response;
response = response[0];
if(response == "X" || response == "x") break;
if(response == "I" || response == "i") {
	inBank = 0;
	cout << "Amount in bank: ";
	cin >> inBank;
	if(inBank <= 0) continue;
	cout << "Days: ";
	cin >> days;
	if(days <= 0) continue;
	origDays = days;
	for(;days>0;days--) {
	cout << "--After " << origDays - days + 1 << " Days(s)--" << endl;
	// This is the way I figure out interest in my game, ignore it.
    millions = inBank / 1000000;
	if(millions < 1) millions = 1;
	interest = inBank * ((3 / sqrt(millions)) / 100);
	// End interest calculation
	cout << "Amount of interest: " << interest << endl;
	inBank += interest;
	cout << "Total in bank: " << inBank << endl;
	}
}
if(response != "X" && response != "x" && response != "I" && response != "i") cout << "Invalid choice." << endl;
}
cout << "Exiting." << endl;
}

It runs pretty smoothly, except for one thing. If you enter in a string where cin places the response into an integer, the script goes crazy. Every time it reaches a cin, it skips over it as if someone had just hit enter. Therefore, it gets caught in an endless loop of printing out the "press i or x" message, and it has to be stopped the hard way. Is there any way to prevent this? Thanks.

dsmith · #2 08-Feb-2004, 11:34

Hello trs2988. Are there really 2987 other trs's here? J/K

Anyway, you are probably blowing out your memory allocation, by trying to place a string into an integer. I would use fgets in this situation, but for more c++ syntax use getline. It is pretty well covered in this thread. cin and the equivalent c command scanf are kind of weak in these situations.

Then your input will always be a string, then when you want to convert it, use a atoi routine.

Also, one more comment. You may want to look at using a double for alot of your variables like inbank & interest. There is also a command called atof that will convert a string to a double.

Hope this helps.
d

trs2988 · #3 08-Feb-2004, 11:50

Alright, I changed my code, but now I'm having other problems. Here's the new file:

CPP / C++ / C Code:

#include <stdio.h>
#include <iostream.h>
#include <stdlib.h>

int main() {
string response;
string temp;
int inBank;
int millions;
int interest;
int days;
int origDays;
while(1) {
cout << endl << "Type I to calculate interesting, or X to exit: ";
cin >> response;
response = response[0];
if(response == "X" || response == "x") break;
if(response == "I" || response == "i") {
	inBank = 0;
	cout << "Amount in bank: ";
	cin.getline(temp,10);;
	inBank = atoi(temp);
	if(inBank <= 0) continue;
	cout << "Days: ";
	cin.getline(temp,3);
	days = atoi(temp);
	if(days <= 0) continue;
	origDays = days;
	for(;days>0;days--) {
	cout << "--After " << origDays - days + 1 << " Days(s)--" << endl;
	// This is the way I figure out interest in my game, ignore it.
    millions = inBank / 1000000;
	if(millions < 1) millions = 1;
	interest = inBank * ((3 / sqrt(millions)) / 100);
	// End interest calculation
	cout << "Amount of interest: " << interest << endl;
	inBank += interest;
	cout << "Total in bank: " << inBank << endl;
	}
}
if(response != "X" && response != "x" && response != "I" && response != "i") cout << "Invalid choice." << endl;
}
cout << "Exiting." << endl;
}

But now I get the following errors:

Borland C++ 5.5.1 for Win32 Copyright (c) 1993, 2000 Borland
interest.cpp:
Error E2285 interest.cpp 21: Could not find a match for 'istream::getline(string,int)' in function main()
Error E2285 interest.cpp 22: Could not find a match for 'atoi(string)' in function main()
Error E2285 interest.cpp 25: Could not find a match for 'istream::getline(string,int)' in function main()
Error E2285 interest.cpp 26: Could not find a match for 'atoi(string)' in function main()
*** 4 errors in Compile ***

Does that mean it can't find the functions? Do I have to include another file? I thought the only one for those functions was stdlib.h.

dsmith · #4 08-Feb-2004, 12:00

trs2988.

I think the problem is that you are passing both of these functions a string and not a char *. While the string class can do a lot of cool things, it can not replace a char *. You have 2 options. Either convert the string to a char * with the string class or just declare a char * to begin with. (#2 option is by far easier

)

CPP / C++ / C Code:

char input[MAX_SIZE+2];   //MAX_SIZE should be defined by #define

cin.getline(input,MAX_SIZE);
atoi(input);

PS - Just to take the blame for this, I did say a string in my first post

trs2988 · #5 08-Feb-2004, 12:05

Thanks! It worked! You have no idea how much that little problem was bugging me.

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