C Board - C Programming

trouble with scanf and validating input

fazio93 — Tue, 21 May 2013 17:30:50 GMT

I need to use scanf to input an 8 digit number with no extra "junk" characters after the number (e.g. 12345678k), just the number, or else a prompt to re-enter. i know scanf isn't recommended but this is the second week of class and it's the only function of its kind we've learned so far ( besides getchar() for flushing the input buffer).

this is what i have so far:

Code:

/* 

   This program prompts the user to setup a pin

   It handles invalid input properly 

*/



#include 



/* Complete the code for this program below */



int main()

{

    int acctNum, pinNum, temp, numDigits = 0;

    char ch;



    printf("Please enter your 8 digit account number: ");

    scanf("%d%c", &acctNum, &ch);

    

    /* Calculates numbers of digits in number entered */

    temp = acctNum;

   while(temp)

    {

      temp = acctNum/10;

      numDigits++;

   }



    while(numDigits != 8 || ch != '\n')

    {

        /* Flushes input buffer */

        while(getchar() != '\n');

    

       printf("Invalid account number. Account number must be 8 digits.\n\n");

        printf("Please enter your 8 digit account number: ");

        scanf("%d%c", &acctNum, &ch);

        

        /* Calculates numbers of digits in number entered */

        while(temp)

       {

         temp = acctNum/10;

         numDigits++;

      }

    }

    

    return 0;

}

problem is, i think i'm having trouble with the \n and scanf. here's what happens:

If i input valid number first time = program ends succesfully

If i input an invalid number first try (e.g. 123456789), i must press twice and then it prompts me to re-eneter, but every input after that is returned as invalid even if it is valid ( i also must press twice for all these inputs).

where am i going wrong?

thanks

Newbie Question

izqomar — Tue, 21 May 2013 15:32:45 GMT

Hello. I'm still pretty new to programming, and new to this board.

Just have a question from a textbook. The code works, but I'm a little confused about the control flow.

Here's the code (actually, just a function from a larger hotel room reservation example program)

Code:

 int find_room(struct hotel *h){



int i;

for(i=0; i<10; i++){

    if(h->rooms[i] == 1)

        return i;}



return -1;



}

My question is. The way it looks to me, it appears that return -1 will be returned no matter what. Obviously, this is not the case, because the program when run does (seem) to work correctly.

So I can only assume that the way it is written, despite the way it *appears* to me that it logically should work, that -1 is only returned if the if statements return i DOESN'T get returned? Is that correct?

I'd just never seen a function with two return statements, unless there was an else following that if statement, to pick one of the two, which there isn't. I guess that's why it seems strange to me.

Any clarification / input appreciated.

Thanks!

For static variables when the memory will be allocated?

raghu_ — Tue, 21 May 2013 08:42:23 GMT

Hi

For static variables when the memory will be allocated? During compilation or linking or loading time?

In below program i am getting error ( error C2099: initializer is not a constant in microsoft visual studio) . If i initialize x = 10 or any constant it works , why? Please help me in this issue

Code:



main() { 

int i=10; 

static int x = i;//error ? 

if(x==i) 

printf("Equal"); 

else if(x>i) 

printf("Greater"); 

else printf("Lesser"); 

return 0; 

}

thanks
raghu

Help w/ Multiple Client Socket Programming (UDP)

Peanutty — Tue, 21 May 2013 07:14:19 GMT

Hi guys, I need some help with socket programming using UDP. I had successfully connected to a server run by another host, but my problem now is to be able to chat with other users or clients in that server. I'm not sure if my messaged actually got through to the user when prompted. Need some help heading in the right direction.. Thank you! Here are my codes for the client webchat:

Code:



/* variables used */ 

int i; //the very famous for-loop counter 

int check; //this variable store the return values of sendto and receive functions to make sure transmission is correct 



char username[16]; 

int userfound; //flag that is set to 1 when user name type in exists 

char message_sent[MAX_MSG_LEN]; 

int len; //message length 

int UDP_socket; s

truct sockaddr_in chateeAddr; //address of user you want to chat to 

char prompt[10]; //user response when asked to continue chatting





/*the first step is to get a UDP socket */ 

UDP_socket = socket(AF_INET, SOCK_DGRAM, 0); char b1[100], b2[100]; 





//the second step is to store the information of server inside 

the chateeAddr structure, 

bzero((char *)&chateeAddr,sizeof(chateeAddr)); chateeAddr.sin_family = AF_INET; 

chateeAddr.sin_port = UDPchatee.portnumber; chateeAddr.sin_addr.s_addr = UDPchatee.userIP; memset(chateeAddr.sin_zero, '\0', sizeof chateeAddr.sin_zero); 

int n = sizeof(chateeAddr); 



while(1) { 

//get message you want to send 

printf("Enter a line of text as your message \n"); gets(b2); 

printf("You entered: %s", b2); sendto(UDP_socket,message_sent,sizeof(message_sent),0,(struct sockaddr *)&chateeAddr,n); 



if(strcmp(b2,"end")==0) 

break; recvfrom(UDP_socket,b1,sizeof(b1),0,NULL,NULL); printf("\nReply:%s",b1); } 



//the final steps is to shut down and close connection shutdown ( UDP_socket , 2 ); 

close ( UDP_socket ); 

for (i = 0; i<10; i++) 

prompt[i] = '\0'; 

printf("Please type 'exit' to exit, or anything else to continue chattingg\n"); 

fgets(prompt, MAX_MSG_LEN, stdin); 



if (strcmp(prompt, "exit\n") == 0) 

break; //close the UDP socket and exit 

} 

close ( UDP_socketID ); 

return 0; 

}

Code:

Function within a function

arti — Tue, 21 May 2013 06:12:44 GMT

I'm thinking of making a function that passes functions as parameters. I'm not sure how to do it though...this is my stab at it.

Code:

void CalcOps(void ovtHrs(&record[i].hrs_wrk, &record[i].ovt_hrs, record[i].hrs, &record[i].gross, record[i].payrate), void calculatetaxes(record[i].gross, record[i].deferred, &record[i].ft, &record[i].st, &record[i].ssi), void netPay(record[i].gross, record[i].deferred, record[i].ft, record[i].st, record[i].ssi, &record[i].net), void calcAccumulator(&tot_payrate, record[i].payrate, &tot_hrs_wrk, record[i].hrs_wrk, &tot_ovt, record[i].ovt_hrs, &tot_gross, record[i].gross, &tot_ft, record[i].ft, &tot_st, record[i].st, &tot_ssi, record[i].ssi, &tot_deferred, record[i].deferred, &tot_net, record[i].net), void calcAverage(tot_payrate, &payrate_avg, tot_hrs_wrk, &hrs_wrk_avg, tot_ovt, &ovt_avg, tot_gross, &gross_avg, tot_ft, &ft_avg, tot_st, &st_avg, tot_ssi, &ssi_avg, tot_deferred, &deferred_avg, tot_net, &net_avg));

Or do i just pass the variables in the functions?

Need help keeps looping

akira124xd — Tue, 21 May 2013 05:21:55 GMT

Code:

#include 



int main()

{ 

    int account;

    char name[ 30 ];

    double balance;

    double amount; 

    FILE *ofPtr;

    FILE *tfPtr; 

    

    ofPtr = fopen( "oldmast.dat", "w" ); 

    tfPtr = fopen( "trans.dat", "w" );

    

    printf( "Sample data for file oldmast.dat:\n" );

    printf( "Enter account, name, and balance (EOF to end): " );

    

    while ( scanf( "%d%[^0-9-]%lf", &account, name, 

        &balance ) != EOF ) { 

        

        fprintf( ofPtr, "%d %s %.2f\n", account, name, balance );

        printf( "Enter account, name, and balance (EOF to end): " );

    }

    

    fclose( ofPtr );

    

    printf( "\nSample data for file trans.dat:\n" );

    printf( "Enter account and transaction amount (EOF to end): " );

    

    while ( scanf( "%d%lf", &account, &amount ) != EOF ) { 

        

        fprintf( tfPtr, "%d %.2f\n", account, amount );

        printf( "Enter account and transaction amount (EOF to end): " );

    }

    

    fclose( tfPtr );

    

    return 0;

}

keeps looping whenever i input EOF

Having problem with ADC display on PIC18F4520 LCD

caramelz — Tue, 21 May 2013 05:04:44 GMT

Hi, I'm having some problems on interfacing ADC with LCD display. The main purpose of using ADC is because I need to read the voltage of the batteries and transfer it, and display to LCD. I'm using MCC18 compiler. Please guide or help me!

Code:

include 

#include 

#include  





void Init_LCD(void);    //Initialise the LCD

void W_ctr_8bit(char);  //8-bit Control word for LCD

void W_data_8bit(char); //8-bit Text Data for LCD





ADCON0=0b00000001;    

ADCON0bits.GO = 1;        // Start ADC 

Delay10TCYx(5); //give channel time to initiliase 

while(ADCON0bits.DONE); // Wait for conversion to finish. 

counts=ADRESH*255 +ADRESL; 

//for 3.62 volts, expect a count of 741 

millivolts = (counts * 1.367)/100; //gives a result of 3630.9 

    Init_LCD();

    W_ctr_8bit(0x80);

    for(i=0;i<8;i++)

    W_data_8bit(MESS3[i]);

    W_ctr_8bit(0x8C);

    W_data_8bit('V');





itoa(millivolts,Distance1); //(int value, char * str, int base); 





W_ctr_8bit(0x89);        

while(Distance1[i])

    {

        W_data_8bit(Distance1[i]);

        i++;

    }

Need help Just Keeps looping

akira124xd — Tue, 21 May 2013 04:56:11 GMT

Code:

#include 



int main()

{ 

        int account;

        char name[ 30 ];

        double balance;

        double amount; 

        FILE *ofPtr;

        FILE *tfPtr; 

        

        ofPtr = fopen( "oldmast.dat", "w" ); 

        tfPtr = fopen( "trans.dat", "w" );

        

        printf( "Sample data for file oldmast.dat:\n" );

        printf( "Enter account, name, and balance (EOF to end): " );

        

        while ( scanf( "%d%[^0-9-]%lf", &account, name, 

                &balance ) != EOF ) { 

                

                fprintf( ofPtr, "%d %s %.2f\n", account, name, balance );

                printf( "Enter account, name, and balance (EOF to end): " );

        }

        

        fclose( ofPtr );

        

        printf( "\nSample data for file trans.dat:\n" );

        printf( "Enter account and transaction amount (EOF to end): " );

        

        while ( scanf( "%d%lf", &account, &amount ) != EOF ) { 

                

                fprintf( tfPtr, "%d %.2f\n", account, amount );

                printf( "Enter account and transaction amount (EOF to end): " );

        }

        

        fclose( tfPtr );

        

        return 0;

}

Issue with random numbers

Paul Omans — Tue, 21 May 2013 03:04:06 GMT

Code:

#include 

#include 

#include 



int xPosCalc(int sigmaMatter, int muMatter, int sigmaAntimatter, int muAntimatter, int xRand)

{

    xRand = rand() % 36;

    int xPosMatter = (1/(sigmaMatter*sqrt(2*M_PI)))*exp(-((xRand-muMatter)*(xRand-muMatter))/(2*(sigmaMatter*sigmaMatter)));

    int xPosAntimatter = (1/(sigmaAntimatter*sqrt(2*M_PI)))*exp(-((xRand-muAntimatter)*(xRand-muAntimatter))/(2*(sigmaAntimatter*sigmaAntimatter)));

    int xProbability = xPosMatter * xPosAntimatter;

    printf("Random variable is: %d", xRand);

    printf("\nProbability is: %d", xProbability);

}



int main(void)

{

    int sigmaMatter = 4.2;

    int muMatter = 27.0;

    int sigmaAntimatter = 6.0;

    int muAntimatter = 17.0;

    int xRand = 0.0;

    xPosCalc(sigmaMatter, muMatter, sigmaAntimatter, muAntimatter, xRand);

}

The problem is my random variable (restricted from 0-35) comes out as 29 every time I run the program, not a random number like I need. I'm guessing this is either a problem with the way I'm passing my variables (something I'm still learning) or a stack error.

I know my math can be simplified, but I don't think that is what's causing the current issue.

operators in switch statements?

SCRIPT_KITTEH — Tue, 21 May 2013 00:12:26 GMT

Hi folks,

So I'm learning about this switch thing. It seems like a cool, clean alternative to a bunch of if's and else if's. I have one question though. In the tutorial on this site concerning switch it says this:

Quote:

Switch case statements are a substitute for long if statements that compare a variable to several "integral" values ("integral" values are simply values that can be expressed as an integer, such as the value of a char).

So does that mean switch statements can only test if variable == value and nothing more, like > < >= <= != etc... ? I tried to make a program to test this and it seems like switch statements are limited to == but I'm not sure, maybe I'm doing something wrong.

This is the program I tried to make to test this:

Code:

#include 



int main () {



        int n;



        printf ( "\nEnter a number to test dis shiet.\n\n" );

        scanf ( "%i", &n );



        switch ( n ) {

                case 0:

                        printf ( "\nYou entered 0.\n" );

                        break;

                case  > 0:

                        printf ( "\nYou entered a number > 0.\n" );

                        break;

                case  < 0:

                        printf ( "\nYou entered a number < 0.\n" );

                        break;

                default:

                        printf ( "\ndafuq?\n" );

                        break;

        }



        return 0;

}

The compiler said this:

Quote:

switchtest.c: In function 'main':
switchtest.c:22:9: error: expected expression before '>' token
switchtest.c:22:9: error: expected expression before '>' token
switchtest.c:25:9: error: expected expression before '<' token
switchtest.c:25:9: error: expected expression before '<' token

So is it true that switch statements only work with the built in == operator? :frown: if that was the case then I would feel rather meh about switch statements.

Question about FILES

evinda — Mon, 20 May 2013 23:24:22 GMT

Hi!!!!I have a question...Why,when I try to run the following code,although I have saved a txt file named "m.txt",I get the message I couldn't open m.txt for writing.?????I hope someone can help me!!!!!Thanks in advance!!!!!

Code:

#include 

#include 





int main()

{

FILE *fp;

int i;

fp = fopen("m.txt", "w");

if (fp == NULL) {

printf("I couldn't open m.txt for writing.\n");

exit(0);

}





for (i=0; i<=10; ++i)

fprintf(fp, "%d, %d\n", i, i*i);





fclose(fp);





return 0;

}

Doubt reagarding use of const variable

AbhinavBajpai — Mon, 20 May 2013 18:14:28 GMT

Hi please tell me what shud be the result of following piece of code and why?

Code:

#include<..> //Consider all includes correctly

main()

{

int i;

const int j;

int *p, *q;

*p = i;

*q = j;

*p++;

*q++;

printf("%d\t%d\t%d\t%d", *p, *q, i, j);



}

p.s. - ignore any syntax error. I hope you must have understood the real doubt of mine.
Thanks.

Adding a constant to multiple variables

melia789 — Mon, 20 May 2013 17:46:11 GMT

Hi,

I was hoping someone could help me with this problem.

Instead of using:

Code:

x=x+k

y=y+k

z=z+k

Is there a more elegant method of adding the same constant to many variables?

Something like:

Code:

(x, y, z) = (x, y, z) + k ??

I tried searching for a solution but couldn't find what I was looking for.

Thanks for any help

Makefile for a single file

ilans11il — Mon, 20 May 2013 13:04:26 GMT

Hi,

I'm trying to create a Makefile for a single fie ( mycod.c)
Could you please help me with the syntax?

thanks

Vectorization

�berfuzz — Mon, 20 May 2013 10:11:46 GMT

I'm trying to learn how o implement vectorization. Please help me with a hello world kind of thing...

Lets say I have this an array like this.

Code:

int Array[10] = { 3,4,5,3,4,5,6,7,8,9};

If I traverse through the array and preform some simple calculation like adding numbers, how would I go about vectorizing this feat? For example if I want to add numbers, .

An example, add element at index 5,6,7 to element with index 1.

Code:

0 1 2 3 4 5 6 7 8 9 --- index

3,4,5,2,8,2,3,5,1,2 --- ints

Thanks!