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Jul 16th, 2009

Problem in understandting Multi dimensional array and nested loops

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hey guys i know its kinda noobish not to understand them since i been coding for 1 month but there rlly some stuff which confuses me in multidimensional array and nested loops like here in this program
I wanted to know if i sum up like in the array for example num[5][10] i wanted to know which get summed first if i did total+=num[x][i]; but here in this program i made i got weird error which i think shouldn't produce it so please someone enlighten me because till now i understand all stuff pointers memory management and hard stuff in C but i don't understand these multi and nested loops

C Syntax (Toggle Plain Text)
#include <stdio.h>
int main(void)
{
    int num[2][3]= {
    {1,1,1},{1,1,1}
    };
    int i;
    int x;
    int total=0;
    for(i=0;i<2;i++) 
       for(i=0;i<3;i++) {
            total+=num[i][x];
            }
       printf("%d",total);
    return getchar();
}
#include <stdio.h>
int main(void)
{
    int num[2][3]= {
    {1,1,1},{1,1,1}
    };
    int i;
    int x;
    int total=0;
    for(i=0;i<2;i++) 
       for(i=0;i<3;i++) {
            total+=num[i][x];
            }
       printf("%d",total);
    return getchar();
}

shouldnt it produce 6 ? please someone enlighten me in understanding this ....

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MrNoob

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Jul 16th, 2009

Re: Problem in understandting Multi dimensional array and nested loops

you got both loops fighting over the same index 'i'

jephthah

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Jul 16th, 2009

Re: Problem in understandting Multi dimensional array and nested loops

the error is probably due to the fact that 'x' isn't initialized, so it's value is something like negative eleventy thousand, causing your program to crap the bed when it uses it as one of the array indices.

jephthah

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Jul 16th, 2009

-1

Re: Problem in understandting Multi dimensional array and nested loops

You have an (i) problem.
You need to use two different variables within a nested loop, such as i and j.

C Syntax (Toggle Plain Text)
   for(i=0;i<2;i++) 
//       for(i=0;i<3;i++) {
         for(x = 0; x < 3; x++ ) {
            total+=num[i][x];
            }
   for(i=0;i<2;i++) 
//       for(i=0;i<3;i++) {
         for(x = 0; x < 3; x++ ) {
            total+=num[i][x];
            }

wildgoose

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Jul 16th, 2009

Re: Problem in understandting Multi dimensional array and nested loops

Whats with return getchar() ? You got several other ways to pause the output.Use one of them rather than this because even though you return some random character as the return of main and exit the OS thinks that the process didn't terminate properly because of a non zero return value.Which of course doesn't cause any problem here but would definitely cause great problems in future when you write some important code.
So better correct it now.

csurfer

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Jul 17th, 2009

-1

Re: Problem in understandting Multi dimensional array and nested loops

Find the corrected code.nothing to wierd about this.try to find out values of each elemnts manuall before
writing the code.

C Syntax (Toggle Plain Text)
#include <stdio.h>
int main(void)
{
    int num[2][3]= {
    {1,2,3},{4,5,6}
    };
    int i;
    int x;
    int total=0;
    for(i=0;i<2;i++) 
      [RED] for(i=0;i<3;i++)[/RED] //here i  SHOULD BE x
           {
            total+=num[i][x];
            }
       printf("%d",total);
    return getchar();
}
 
int num[2][3]= {
    {1,2,3},{4,5,6}
    };
#include <stdio.h>
int main(void)
{
    int num[2][3]= {
    {1,2,3},{4,5,6}
    };
    int i;
    int x;
    int total=0;
    for(i=0;i<2;i++) 
      [RED] for(i=0;i<3;i++)[/RED] //here i  SHOULD BE x
           {
            total+=num[i][x];
            }
       printf("%d",total);
    return getchar();
}

int num[2][3]= {
    {1,2,3},{4,5,6}
    };

Value assinged like this:
===========================
num[0][0]=1;
num[0][1]=2;
num[0][2]=3;
num[1][0]=4;
num[1][1]=5;
num[1][2]=6;

assign the range of loop variables according to this.1st do a dry run in case of multiD arrays.

Thanks,
DP

Last edited by Dream2code; Jul 17th, 2009 at 4:05 am.

Dream2code

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Jul 17th, 2009

Re: Problem in understandting Multi dimensional array and nested loops

yah i know now but what if i wanna count like row by row like
{1,3,4} {3,5,6} it will count 1 + 3 and 3+5 and 6 + 4 ?
should i switch variables x first then i 2nd ?

MrNoob

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Jul 17th, 2009

Re: Problem in understandting Multi dimensional array and nested loops

Click to Expand / Collapse Quote originally posted by csurfer ...

Whats with return getchar() ? You got several other ways to pause the output.Use one of them rather than this because even though you return some random character as the return of main and exit the OS thinks that the process didn't terminate properly because of a non zero return value.Which of course doesn't cause any problem here but would definitely cause great problems in future when you write some important code.
So better correct it now.

well for getchar() coz sometimes i use dev when testing a program its a habbit of me to put return getchar(); rather than writing small thing since its a program made for learning

MrNoob

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Jul 17th, 2009

Re: Problem in understandting Multi dimensional array and nested loops

Click to Expand / Collapse Quote originally posted by MrNoob ...

well for getchar() coz sometimes i use dev when testing a program its a habbit of me to put return getchar(); rather than writing small thing since its a program made for learning

Too lazy to just split them up like this?

C Syntax (Toggle Plain Text)
getchar();
return 0;
getchar();
return 0;

It's better to return a fixed value when your program has exited successfully because in your current program, the return value depends on what key the user has pressed, not a very good habit IMO.
If you just write it like: return getchar(); , how can you know then whether your program has exited successfully or not?

Last edited by tux4life; Jul 17th, 2009 at 9:53 am.

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Jul 17th, 2009

Re: Problem in understandting Multi dimensional array and nested loops

how can i chk if it exited successfully is there a way to chk program return value ?

MrNoob

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