Thread: Simple check/deposit exercise in C

I'm teaching myself C atm, reading online tutorials and doing exercises at the end of the chapters. What I've written is a program that reads in either check/deposit and adjusts the amount in the bank account. For example, deposit 1000, deposits 1000 in the bank.

Explanation of some of the code:

The function separator is used to separate the command "deposit/check" from the amount to deposit. How it does this is it will scan the input string for letters and put it in a char array. To scan the amount to deposit in the same line, the loop also searches for char numbers and converts it to an int within the same loop. The function also compares user input to the strings "check" and "deposit".

The function mystrcmp works like strcmp.

Here is the code:

Code:

#include <stdio.h>

int bankAccount = 1000;

main()
{
	int i, c;
	char input[25];
	
	while ( 1 )
	{
		printf("Enter a check or deposit with the amount or 'q' to quit: ");	
		
		if ( (c = getchar() ) == 'q' )
			break;
		
				
		getLine( input, 25 );		        //gets input
		separator( input );		        //separates command and amount
		
		printf("Balance: %d\n", bankAccount);   //prints the balance after each loop
		
	}
}

//Reads the input line
int getLine( char array[], int max )
{
	int i = 0; 				        //incrementer
	int c;					        //holds char
	max = max - 1;					//for null zero
	
	while ( (c = getchar() ) != EOF )
	{
		if ( c == '\n')				//if end of line, break
			break;
		if ( i < max )				//if less than max, put in array
		{
			array[i] = c;
			i++;
		}
		
		if ( (c == EOF) && (i == 0) )
			return EOF;
		
	}
	
	array[i] = '\0';				
	return i;
}


int separator( char array[] )
{
	char command[20];				//will hold either deposit or check
	char amount[20];				//holds amount, but in char
	char deposit[] = "deposit";				
	char check[] = "check";			
	int i, digit, num, retVal = 0;

	for ( i = 0; array[i] != '\0'; i++ )
	{
		if ( array[i] >= 97 && array[i] <= 127 )	//if between a-z, no caps
		{
			command[i] = array[i];		        //put letter in array
			printf("Entered %s\n", command);
		}
		if ( array[i] >= 48 && array[i] <= 57 )		//if between 0-9
		{
			amount[i] = array[i];
			digit = amount[i] - '0';	        //converts character int to
			retVal = retVal*10 + digit;	        //actual int, i.e. '123' 
		 }                                                    					   
	}

	printf("Entered %s\n", command);			//test commands to debug
	printf("Entered %d\n", retVal);			        //test commands to debug

	if ( mystrcmp( command, deposit ) == 0 )
	{
		bankAccount = bankAccount + retVal;	        //add to bank account 
	}
	
	if ( mystrcmp( command, check ) == 0 )
	{
		bankAccount = bankAccount - retVal;	        //subtract from bank
	}
		
	return 0;
}

//This is my personal string comparison function.
mystrcmp(char str1[], char str2[])					
{
	int i = 0;

	while(1)
	{
		if(str1[i] != str2[i])
			return str1[i] - str2[i];
		if(str1[i] == '\0' || str2[i] == '\0')
			return 0;
		i++;
	}
}

So my problems are:

1) The if statement to quit the program reads the first letter and if it is 'q', then the program exits. But what happens is that if I type "deposit", it reads the first char 'd' and then passes off 'eposit' to the function below. How do I overcome this?

2) I have no idea what's going on here, command[20] does not work, but command[10] does. Must be something with the length of the array.
Here is an output with command[20]:
Enter a check or deposit with the amount: check 1000
Entered cX���
Entered ch���
Entered che��
Entered chec�
Entered check
Entered check
Entered 1000
Balance: 1000

Here is an output with command[10]:
Enter a check or deposit with the amount: check 1000
Entered c
Entered ch
Entered che
Entered chec
Entered check
Entered check
Entered 1000
Balance: 0


I think what I've done here is make a simple program overcomplicated. Nevertheless, I would like to debug it first, then rewrite the code so that it's more logical.

Thanks for taking the time to read this.

A couple things first:

• It's int main(void) and return an int at the end.
• Always specify a return type and parameter list (or lack there of) for your functions explicitly. That is, mystrcmp needs an explicit "int" in front of it.
• Either define your functions before you use them, or put a prototype at the top of the file

The first two things on there make me think some of the tutorials/books you're using are a bit outdated, so be wary.

As for your "eposit" issue, getchar removes the letter from the input buffer, so when you call it in the if statement you highlighted, you remove the first letter, whether it's a 'q', a 'd' or anything else. You need to call getLine first, then check if input[0] is a 'q'.

Originally Posted by edishuman

Well what I was told was to use character scanning and scan strings one by one. It has definitely helped me realize what happens in the process of reading strings. I have learned of the scanf() function as well, but was told not to use it, the reason being it was prone to cause errors for beginner's learning C. How valid that statement is I do not know, but I've rather liked learning this process of scanning characters. Can anyone clarify as to why this is so? I probably will begin using scanf() from now on seeing how it will save me much more time.

If your instructions say go char by char, then do so. But heed the last paragraph in my original reply. It tells you how to rearrange your code to avoid your "eposit" issue. If you aren't supposed to do that, look at the ungetc() function, but remember, you are only guaranteed the ability to put back 1 char.

scanf is something like a "with great power comes great responsibility" function. It allows you a lot of flexability in getting input, but you can screw up the format string easily. It's better used for formatted data, like from a file, or for parsing strings read with fgets. One of the big complaints is how scanf handles different data types. For example, the %c modifier is the only one that actually stores a white space character (space, tab, new line, etc). The %[] modifier can store a white space character depending on what you put inside. Also, scanf is notorious for leaving the newline in the input buffer after you read a number, so many newbies read an int with %d, then wonder why their %c didn't work (hint, it grabbed the newline from when they hit enter after their int).

Also, can anyone tell me what I'm doing wrong with my array? I can't seem to find the problem.

I assume you mean the second problem you were having, with your command array printing garbage. Take another look at Quzah's first reply:

Originally Posted by quzah

command is not a qualified string. It's just an uninitialized array. It's pure luck that it "worked" with its size as 10.

I added the color to draw your attention to the important parts. It's not qualified, because it's not null terminated at every step. There are no nulls in there to tell printf when to stop printing. He said it's uninitialized, so initialize it:

Code:

char command[20] = {0};  // set command to all nulls

If anyone is interested, this is where I learn most of my C programming from C Programming Notes

Not a bad site, but a bit outdated. It's meant to supplement K&R's "The C Programming Language" (which was written in the early 90s), and the site itself dates from 95-96.