short matrix problem

In this program I only input the number of columns and the entries of the matrix. The program then determines the number of rows. The program works perfectly for the correct number of entries like 4 entries for a 2 by 2 matrix. However it doesnt work for 3 entries for a 2 by 2 matrix. Please reply fast

Code:

---

---

Code:

---

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


int  main()
{
  int m,x, n, c = 0, d,k, matrix[10][10], transpose[10][10], product[10][10];


  printf("Enter the number of columns of matrix ");
  scanf("%d",&m);
  if(m<=0){
    printf("You entered a invalid value.");
    exit(0);
  }
  else{
    printf("Enter the elements of matrix \n");


    for( c = 0 ; c < 10 ; c++ )
      {
        for( d = 0 ; d < m ; d++ )
          {
            scanf("%d",&matrix[c][d]);
            if (matrix[c][d] == 99) // 99 is  variable I declared to use as a break
          break;




          }
        if (matrix[c][d] == 99)
          break;
      }
  }


  printf("\nHere is your matrix:\n");
  int i;


  for(i=0;i<c;i++)
    {
      for(d=0;d<m;d++)
        {


 printf("%3d ",matrix[i][d]);
        }
printf("\n");
    }

---

Quote:

---

Originally Posted by kiwi101

Please reply fast

---

fast

(If I wanted to be nasty, I would have let my reply stop here, but I'll be kind. Next time, don't insist that people "reply fast".)

Quote:

---

Originally Posted by kiwi101

However it doesnt work for 3 entries for a 2 by 2 matrix.

---

How does it not work? Also, you should indent your code properly to make it easier to read.

Do you want an m x m, or a 10 x m matrix?

u miss fflush()... u need to clear ur buffer rite after input from user else ur next scanf will still take ur previous entered number as input(in the case that next scanf very close together)


question for u: are u on a open book test or something? :cool:

sorry :(
i was just getting tensed since ive bin working on this for ages and i cant get any ideas

it does work if i put 3 entries but not the way it shoud like itll give me garbage values.

no im not i just have this due in a couple of hours.

Could u elaborate? ive neve rused fflush

Okay I have an idea I just dont know how to quite put it down. If the user doesnt enter m*n entries then the program should just exit
kindof like this

Code:

---

if(m*c%m != 0){
            printf("NO");
            exit(0);
          }
            else{
print

---

Why haven't you answered laserlight's or TheBigH's questions?

Neko Tan doesn't know what it's talking about. fflush is not needed.

Indent your code properly. Look at post #7. Is that really how you mean your code to look?

I did reply to laserlight.
Look im just trying to brainstorm i want the matrix to be a m*n matrix.
i want my code to exit if the user doesnt enter m*n values.
Could you please give me some direction?
Im waitng here

If it's supposed to be m x n why don't you set n to anything? You're not even using it.

m = # of rows
in this program my # of rows is called c

n= # of columns
in this program my # of colums is called m

so a c*m matrix

Could you guys please not make fun of me and help me plz

Yes, I see your stressed out, so I deleted my funny post.

Quickly, what's the problem?

Your variable names are terrible. Why is n called m and m called c???

Anyway, I think I'm beginning to understand what you're up to here. You want the user to enter the number of columns (but NOT the number of rows). Then the user inputs rows of data until they decide to stop by entering the number 99.

Is that correct?

Can you show an exact example of what doesn't work?

Thanks :)
let me explain it with an example please tell me if you get it
when the user enters 2 as the # of columns. And then enter 1,2,3,4 as the input. The program automatically displays a 2 by 2 matrix with 1,2,3,4 entries. However my problem is that if that same user accidentally only entered 1,2,3 then I want the program to exit using the exit function. But I don't know how to write it properly could you please tell me how i should write it.

Yes you are correct
Letme show u an example

Enter the elements of matrix
1 2 3 4
99


Here is your matrix:
1 2
3 4

BUT:
Enter the elements of matrix
1 2 3
99

Here is your matrix:
1 2

instead of displaying just 1 2 i want the program to say "invald # of entries" and then exit

could you please tell me how to do that?

So you want to ensure that the user enters complete rows.

Two possibilities:

1. Check that the value of d is 0 (i.e., they entered 99 as the first value in a column).

2. Write it so entering the magic number (99) only works if it's the first value in a column.

Code:

---

for (c = 0; c < 10; c++)
{
    scanf("%d", &val);
    if (val == 99)
        break;
    matrix[c][0] = val;
    for (d = 1; d < m; d++)  // note that d starts at 1 here
    {
        scanf("%d", &matrix[c][d]);
    }
}

---

when I enter 1,2,3,4,99 this is what I get back from the code
Here is your matrix:
1 2
3 4
BUT

when i enter 1,2,3,99 this is what i get back
Here is your matrix:
1 2

Code:

---

    for( c = 0 ; c < 10 ; c++ )
      {
        for( d = 0; d < m ; d++ )
        {
            scanf("%d",&matrix[c][d]);
           
            if (matrix[c][d] == 99) // 99 is  variable to use as a break
              break;
             
        }
       
        if (matrix[c][d] == 99)
          break;
      }
   
  }
  if(d<m)
    printf("\nArray data is missing.\n");

---

Detects short rows, (last row only), but won't detect if a full row is missing.

Im so grateful to the two of you but both codes didnt work for me
The problem i have with oogaboogas code is if they enter 99 first how will the program know when the user has finished entering all entries
and the problem with adaks code is for some reason it prints the statement everytime

Is there anyway you guys can write this statement in code and tellme where to place it it might work

Code:

---

if( #ofentries != c*m)
printf("Invalid number of entries);
exit(0);
else{
print

---

How about:

Code:

---

if (d > 0) {
    printf("...");
    exit(1);
}

---

You don't need the else part, since the if part exits.

Quote:

---

Originally Posted by oogabooga

Why haven't you answered laserlight's or TheBigH's questions?

Neko Tan doesn't know what it's talking about. fflush is not needed.

Indent your code properly. Look at post #7. Is that really how you mean your code to look?

---

maybe this happen only on my compiler... it seem like stuck on 2nd scanf (if without fflush)...

OMGSH thankyou soo muchit worked
but yeah i was just reading about fflush online too cuz mine also got stuck on the 2nd scanf

i had one last question sorry to annoy you so much today
i want the program to exit if the user inputs a value in the matrix less than 0. i plan on writing it like

Code:

---

if(matrix[c][d] < 0){
printf("not valid number");
exit(1);}

---

but ive been trying this for a while but i cant seem to understand where exactly in the code i should put it
ive tired numerous times but nothing has worked out

Quote:

---

Originally Posted by kiwi101

i had one last question sorry to annoy you so much today
i want the program to exit if the user inputs a value in the matrix less than 0. i plan on writing it like

Code:

---

if(matrix[c][d] < 0){
printf("not valid number");
exit(1);}

---

but ive been trying this for a while but i cant seem to understand where exactly in the code i should put it
ive tired numerous times but nothing has worked out

---

Code:

---

for( c = 0 ; c < 10 ; c++ )      {
        for( d = 0 ; d < m ; d++ )
          {
            scanf("%d",&matrix[c][d]);
            if (matrix[c][d] == 99) // 99 is  variable I declared to use as a break
          break;
 
          if (matrix[c][d] < 0){
          printf ("not valid number");
          getch();
          exit(1);}
 
 
          }
        if (matrix[c][d] == 99)
          break;
      }
  }

---

check everytime after scanf. sry, im new here... im have no idea how to edit with color on ur code...

Thanks!!!! Its working!

Could you tell me why my multiplication of this matrix and its transpose is coming wrong. Its usually wrong if its not a square matrix.

Code:

---

for( i = 0 ; i < c ; i++ )
    {
      for( d = 0 ; d < m ; d++ )
        {
          transpose[d][i] = matrix[i][d];
        }
    }


  printf("Transpose of entered matrix :-\n");


  for( i = 0 ; i < m ; i++ )
    {
      for( d = 0 ; d < c ; d++ )
        {
          printf("%3d\t",transpose[i][d]);
        }


      printf("\n");
    }
  // printf("The product of matrix and transpose is %d:");
  for( i = 0 ; i < c ; i++ )
    {
      for( d = 0 ; d < m ; d++ )
        {
          product[i][d]=0;
          for(k=0;k<c;k++) {
            product[i][d] = product[i][d] + matrix[i][k] * transpose[k][d];
          }
        }
    }
  printf("\nThe Product Of The Two Matrices Is:\n\n");
  for(i=0; i<c; i++) {
    for(d=0; d<k; d++) {
      printf(" %3d ",product[i][d]);
    }
    printf("\n");
  }






  return 0;

---

The transpose is right its just the multiplication of the matrix and transpose sometimes comes wrong

sorry about the indentation :(

Think about it. Your multiply routine has 3 loops with 3 index variables (i, d and k) that each go from 0 to a certain limit (c, m and c) respectively. You fill your product matrix using product[i][d], so you have

product[0][0]...product[0][m-1]
...
product[c-1][0]...product[c-1][m-1]

That means that your for loop for printing the product matrix should be

Code:

---

for i from 0 to c
    for d from 0 to m

---

The way you currently have it, d stops at k, which (from your multiply loop) remains equal to c. Thus, you are printing c rows and c columns, hence it only working for a square matrix.

EDIT: And this should be a huge, huge clue to just how awful one-letter variable names are. They are only useful for loop indexes, (x,y) coordinates and very simple math equations. Variable names like matrix1_rows, matrix2_cols, product_rows, product_cols would make this much, much clearer, and keep you from making such mistakes. You have been warned...never post such ridiculous stuff here again, or face utter humiliation :p.

So if I use this loop I end up with the right answer but the dimensions arent right so there are like 2 garbage values in the matrix

Code:

---

for( i = 0 ; i < c ; i++ )
    {
      for( d = 0 ; d < m ; d++ )


        {
          product[i][d]=0;
          for(k=0;k<m;k++) {
            product[i][d] = product[i][d] + matrix[i][d] * transpose[i][d];
          }
        }
    }
  printf("\nThe Product Of The Two Matrices Is:\n\n");
  for(i=0; i<c; i++) {
    for(d=0; d<k; d++) {
      printf(" %3d ",product[i][d]);
    }
    printf("\n");
  }

---

Why do you have 2 threads on the same subject?
I'm closing the other one, since it's now got the same code in both of them (with the same replies from different people!)

sorry i made the first one before and I didnt think anyone was replying to it :(

Could you please help me though
I'm freaking out here pleasee!!

Hey salem I saw what you posted by replacing the k with an m and I've already tried that but it not only gives the wrong dimensions but even the values are wrong. As opposed to what I posted up here which only gives the wrong dimensions but right answer.
Please help me think of something

Now its not even posting the right answer anymore
OH CRAP!!

How about posting your current code?

Bye, Andreas

The only problem I see with your program is the terrible variable names you're using.

Quote:

---

And this should be a huge, huge clue to just how awful one-letter variable names are. They are only useful for loop indexes, (x,y) coordinates and very simple math equations. Variable names like matrix1_rows, matrix2_cols, product_rows, product_cols would make this much, much clearer, and keep you from making such mistakes

---

If you use self-evident names, the solution becomes apparent.

My current code:

Code:

---

for( i = 0 ; i < c ; i++ )
    {
      for( d = 0 ; d < m ; d++ )


        {
          product[i][d]=0;
          for(k=0;k<m;k++) {
            product[i][d] = product[i][d] + matrix[i][k] * transpose[k][d];
          }
        }
    }
  printf("\nThe Product Of The Two Matrices Is:\n\n");
  for(i=0; i<c; i++) {
    for(d=0; d<k; d++) {
      printf(" %3d ",product[i][d]);
    }
    printf("\n");
  }

---

what i get when i enter integer 1-15:


Enter the elements of matrix
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 99


Here is your matrix:
1 2 3 4 5
6 7 8 9 10
11 12 13 14 15
Transpose of entered matrix :-
1 6 11
2 7 12
3 8 13
4 9 14
5 10 15


The Product Of The Two Matrices Is:


55 130 205 -847853949 -574877379
130 330 530 -1397410638 46177804
205 530 855 -1946967327 667232987
you see the 3 by 3 matrix is correct how do i get rid of the other 2 columns

Please help!

sorry about the variable name guys please bear with me though! :)

Quote:

---

Originally Posted by kiwi101

you see the 3 by 3 matrix is correct how do i get rid of the other 2 columns

---

Don't print them.

Code:

---

printf("\nThe Product Of The Two Matrices Is:\n\n");
  for(i=0; i<c; i++) {
    for(d=0; d<k; d++) {
      printf(" %3d ",product[i][d]);

---

Why don't you listen to the people here? You have been told several times that your variable names are crap. You are accessing elements in your product-array which have garbage values because you have never set them (and don't need to).

Bye, Andreas

im sorry i know my variable names are crap
how can I not print them?
i tried commenting it out but then it only shows that.
please give me details my brian doesnt seem to be processing since this code has stressed me out way too much

Matrix multiplication - Wikipedia, the free encyclopedia
If you're multiplying a matrix with it's transposition (X,Y) * (Y,X), then the resultant matrix is going to be square (either X,X or Y,Y)

Your output result isn't square.

Which makes me suspect your calculation isn't square either.

1. Initialise your arrays.

Code:

---

  int m, x, n, c = 0, d, k, matrix[10][10] = { { 0 } }, transpose[10][10] = { { 0 } }, product[10][10] = { { 0 } };

---

Then the results are

Code:

---

Enter the number of columns of matrix 5
Enter the elements of matrix
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 99

Here is your matrix:
  1  2  3  4  5
  6  7  8  9  10
 11  12  13  14  15
Transpose of entered matrix :-
  1          6        11       
  2          7        12       
  3          8        13       
  4          9        14       
  5        10        15       

The Product Of The Two Matrices Is:

  55  130  205    0    0
 130  330  530    0    0
 205  530  855    0    0

---

NOW - go through and add some variable names like
int matRows, matCols;
int transRows, transCols;
int multRows, multCols;

Quote:

---

Originally Posted by kiwi101

im sorry i know my variable names are crap

---

Don't be sorry, just change them.

Quote:

---

Originally Posted by kiwi101

how can I not print them?

---

Your condition in the inner for-loop is wrong. You don't want to increment "d" up to "k" (and "m" neither). So what's left, considering that the resulting product-array is square?

Bye, Andreas

And don't play the "I don't have time" game either.
I've just done the renaming in your code, and it took exactly 5 minutes to do - including retesting.

Code:

---

$ ./a.out
Enter the number of columns of matrix 5
Enter the elements of matrix
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 99

Here is your matrix:
  1  2  3  4  5
  6  7  8  9  10
 11  12  13  14  15
Transpose of entered matrix :-
  1          6        11       
  2          7        12       
  3          8        13       
  4          9        14       
  5        10        15       

The Product Of The Two Matrices Is:

  55  130  205
 130  330  530
 205  530  855

---

when i did that i get
55
130
205
0
0
130
330
530
0
0
205
530
855
0
0

when i did what salem told me i get
55
130
205
0
0
130
330
530
0
0
205
530
855
0
0

SORRY FOR MY DUMBNESS!!!
I got it THANKS!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

another question for u guys if instead of 99 is there another way my program can detect that the user is done typing?? what if i do EOF?

Code:

---

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


int  main()
{
  int val, m,x, n, c = 0, d,k, matrix[10][10], transpose[10][10], product[10][10]; //defining variables


  printf("Enter the number of columns of matrix ");
  scanf("%d",&m);
  if(m<=0){  //error checking if user enter negative number or 0 for column
    printf("You entered a invalid value.\n");
    exit(0);
  }
  else{
    printf("Enter the elements of matrix \n");


    for( c = 0 ; c < 10 ; c++) //forst for loop to scan the matrix
      {
        for( d = 0 ; d < m ; d++ )
          {
            scanf("%d",&matrix[c][d]);
            if (matrix[c][d] == 99) // 'x' is character variable I declared to use as a break
              break;
            if (matrix[c][d] < 0){ //error checking if any entries in the matrix are negative
              printf ("you entered an invalid number\n");
              exit(1);}








          }
        if (matrix[c][d] == 99)
          break;
          }
  }


  if (d > 0){ //error checking to make sure the number of entries is correct
    printf("The number of entries is not valid\n");
    exit(1);
  }
  printf("\nHere is your matrix:\n");
  int i; //declaring i to be count for row


  for(i=0;i<c;i++)
    {
      for(d=0;d<m;d++)
        {


          printf("%3d ",matrix[i][d]);
        }
      printf("\n");
    }

---

last question please give some ideas!!

Seriously - stop bumping your own threads every couple of minutes with some pithy "please help".

I was going to say something, but now I'll leave it to the next person to have a go instead.
How To Ask Questions The Smart Way

EOF is a multi-key entry, that most users won't know how to enter.

You could take user entry as a string, and convert it with sscanf(). Then it's simple to stop by entering a letter.

if I use EOF instead of 99 it only works with input files not if the user directly enters it

Quote:

---

Originally Posted by kiwi101

if I use EOF instead of 99 it only works with input files not if the user directly enters it

---

It works perfectly fine with direct user input by typing Ctrl-D (every OS except for DOS/Windows) or Ctrl-Z and enter (only DOS/Windows). Adak is right, though. It's a multi-key input (3 keys for DOS/Windows or 2 for every other OS).

Quote:

---

Originally Posted by kiwi101

if I use EOF instead of 99 it only works with input files not if the user directly enters it

---

That's probably because you're one of the users who doesn't know how to trigger the end of file condition when entering input :)

Try entering CTRL + D or CTRL + Z on a separate line.

At Salem I won't say anything to you cuz you helped me thanks :)
and Adak thanks i know thatll get me started
if I wanted the program to exit if the user has more than 10 rows or 10 columns how would I go about writing that?

thanks i didnt know how to trigger the EOF

if I wanted the program to exit if the user has more than 10 rows or 10 columns how would I go about writing that?

i know how to do 10 columns but rows i guess has some trick

The c variable in the for loop, only goes from 0 to 9, so 10 rows. It will automatically quit and can't run over that amount, unless you change your code.

So I don't know what "trick" you're referring to.

guys i have class in an hour I wont bug u again today
please help me understand how I can exit the program if the user enter more than 10 rows

i want to display an error code myself to the user

You mean if m > 10?

You're tough to nail down here.

well yeah if m>10 i can write that down in the beginning
but what if c >10 (number of rows)

C can't be more than 10:

Code:

---

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

---

okay thanks :)

for the EOF when i enter the value of the input and press CTRL-Z the whole program just stops

Quote:

---

Originally Posted by kiwi101

guys i have class in an hour I wont bug u again today

---

Use the time before and after your class to change the variable names.

I personally won't help you any further if you continue to ignore the advice we give you here.

Bye, Andreas

Don't enter the value, and then enter EOF, at the same time. Enter your values <hit enter>. Next loop, when you want to quit, press the EOF key combo.

I know thats exactly what im doing but its not working
what if instead of 99 i want to assign a * as end of program how would i do that
like char *;

oh and dont worry ill change my variable names

Post your current code, so I can see what's doing.

Are you testing user's entry for EOF?

Code:

---

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


int  main()
{
  int val, m,x, n, c = 0, d,k, matrix[10][10], transpose[10][10], product[10][10]; //defining variables


  printf("Enter the number of columns of matrix ");
  scanf("%d",&m);
  if(m<=0 || m>10){  //error checking if user enter negative number or 0 for column
    printf("You entered a invalid value.\n");
    exit(0);
  }
  else{
    printf("Enter the elements of matrix \n");


    for( c = 0 ; c < 10 ; c++) //forst for loop to scan the matrix
      {
    for( d = 0 ; d < m ; d++ )
          {
    scanf("%d",&matrix[c][d]);
            if (matrix[c][d] == 99) // 'x' is character variable I declared to use as a break
              break;
            if (matrix[c][d] < 0){ //error checking if any entries in the matrix are negative
              printf ("you entered an invalid number\n");
              exit(1);}
          }
            if (matrix[c][d] == 99)
            break;
          }
  }


  if (d > 0){ //error checking to make sure the number of entries is correct
    printf("The number of entries is not valid\n");
    exit(1);
  }
  printf("\nHere is your matrix:\n");
  int i; //declaring i to be count for row


  for(i=0;i<c;i++)
    {
  for(d=0;d<m;d++)
        {


      printf("%3d ",matrix[i][d]);
        }
      printf("\n");
    }

---

my bad

Code:

---

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


int  main()
{
  int val, m,x, n, c = 0, d,k, matrix[10][10], transpose[10][10], product[10][10]; //defining variables


  printf("Enter the number of columns of matrix ");
  scanf("%d",&m);
  if(m<=0 || m>10){  //error checking if user enter negative number or 0 for column
    printf("You entered a invalid value.\n");
    exit(0);
  }
  else{
    printf("Enter the elements of matrix \n");


    for( c = 0 ; c < 10 ; c++) //forst for loop to scan the matrix
      {
    for( d = 0 ; d < m ; d++ )
          {
    scanf("%d",&matrix[c][d]);
            if (matrix[c][d] == EOF) // 'x' is character variable I declared to use as a break
              break;
            if (matrix[c][d] < 0){ //error checking if any entries in the matrix are negative
              printf ("you entered an invalid number\n");
              exit(1);}
          }
            if (matrix[c][d] == EOF)
            break;
          }
  }


  if (d > 0){ //error checking to make sure the number of entries is correct
    printf("The number of entries is not valid\n");
    exit(1);
  }
  printf("\nHere is your matrix:\n");
  int i; //declaring i to be count for row


  for(i=0;i<c;i++)
    {
  for(d=0;d<m;d++)
        {


      printf("%3d ",matrix[i][d]);
        }
      printf("\n");
    }

---

OK, the check is in there. Did you get it working the way you wanted it to?

If not, describe when the EOF test should make the entry of numbers, quit.

I don't suppose you've read the manual page for scanf in all your fumbling around.

man page scanf section 3

Quote:

---

RETURN VALUES

These functions return the number of input items assigned. This can be
fewer than provided for, or even zero, in the event of a matching fail-
ure. Zero indicates that, although there was input available, no conver-
sions were assigned; typically this is due to an invalid input character,
such as an alphabetic character for a `%d' conversion. The value EOF is
returned if an input failure occurs before any conversion such as an end-
of-file occurs. If an error or end-of-file occurs after conversion has
begun, the number of conversions which were successfully completed is
returned.

---

So, begin with
int result = scanf("%d",&matrix[c][d]);
printf("scanf returned %d\n", result );

And observe what you get when you
- type in a number
- type in a letter
- type in your platform specific key sequence (ctrl-d or ctrl-z) to signal EOF

I just wanted to say thank you to everyone here
i finished my project and honestly i would've bin lost without u guys
thank you for taking out the time to help me :)