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I wrote a c++ program to calculate matrix multiplication problem using dynamic programming. I use s[][] to store the places of inserting parentheses. However, I get those errors about using the two dimensional array as parameter:

matrics.cpp:4:38: error: expected ')'
void findtrace(int i, int j, int[][7]s){
                                     ^
matrics.cpp:4:15: note: to match this '('
void findtrace(int i, int j, int[][7]s){
              ^
matrics.cpp:8:17: error: use of undeclared identifier 's'
                printf("%d\t",s[i][j]);
                              ^
matrics.cpp:9:18: error: use of undeclared identifier 's'
            findtrace(i,s[i][j],s);
                        ^
matrics.cpp:10:13: error: use of undeclared identifier 's'
                findtrace(s[i+1][j],j,s);
                          ^
matrics.cpp:42:2: error: no matching function for call to 'findtrace'
        findtrace(1,len-1,s);
        ^~~~~~~~~
matrics.cpp:4:6: note: candidate function not viable: no known conversion from 'int [len][len]' to 'int (*)[7]' for 3rd argument
void findtrace(int i, int j, int[][7]s){
     ^
5 errors generated.

It cost me two hours to debug this; however, I still have that error. Anyone can help me? 

#include <iostream>
using namespace std;

void findtrace(int i, int j, int[][7] s){
    if(i==j)
        printf("%d\t", i);
    else{
        printf("%d\t",s[i][j]);
        findtrace(i,s[i][j],s);
        findtrace(s[i+1][j],j,s);
    }
}

int main(){
    int p[] = {30,35,15,5,10,20,25};
    int len = sizeof(p)/sizeof(p[0]);
    //void findtrace(int[][len]s, int i, int j);
    int m[len][len];
    int s[len][len];
    printf("len p = %d\n",len);
    for(int i=1;i<=len;i++)
        m[i][i] = 0;
    int temp;
    for(int k=1;k<len;++k){
        for(int j=k+1;j<len;++j){
            int i = j-k;
            m[i][j] = m[i][i]+m[i+1][j]+p[i]*p[i-1]*p[j];
            s[i][j] = i;
            for(int t=i+1;t<j;++t){
                if( m[i][t]+m[t+1][j]+p[i-1]*p[j]*p[t]<m[i][j] )
                m[i][j] = m[i][t]+m[t+1][j]+p[i-1]*p[j]*p[t];
                s[i][j] = t;
            }
            //printf("m[%d][%d] = %d\t",i,j,m[i][j]);
        }
    }
    printf("\n%d\n",m[1][len-1]);
    findtrace(1,len-1,s);
}
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5
  • Can you identify what is causing your first error? Do you know what that message means? Commented Jan 17, 2015 at 19:26
  • 3
    When posting questions with code, please don't include line numbers. It makes it much harder to copy-paste the code. Instead mark the lines the question is about in some other way. Commented Jan 17, 2015 at 19:26
  • 2
    Also, are you sure you're programming in C++? the only C++ specific thing in your code is the header <iostream> and using namespace std, everything else is just C (like using printf and variable-length arrays). Commented Jan 17, 2015 at 19:27
  • @JoachimPileborg Sorry for the confusion, I am actually writing in C++ but I am a learner and used some C grammars. Thanks. Commented Jan 17, 2015 at 19:35
  • @DrewDormann I am sorry I am a new C++ programmer and I am not pretty sure about those. Commented Jan 17, 2015 at 19:42

3 Answers 3

Reset to default
1

The first error you have is due to a typo in your syntax for passing the array. It should be:

void findtrace(int i, int j, int s[][7])

not:

void findtrace(int i, int j, int[][7] s)

Also, take a look at this answer.

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1 Comment

Accept a right answer to close the question please. Both answers are correct.
0

The error is here

void findtrace(int i, int j, int[][7] s)

it should be 

void findtrace(int i, int j, int *s[])
                                ^^^

and call it as 

findtrace(1,len-1,(int **)s);

If compiler is C99 compatible

From C99, C language supports variable sized arrays to be passed simply by specifying the variable dimensions

void findtrace(int i, int j, int s[][7])

will be fine also

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7 Comments

Almost right, but your change will cause the function to expect an array of pointers, instead of a pointer to an array. Those two are very different. Also, an array of arrays is not the same as a pointer to pointer, so your cast is wrong too.
@JoachimPileborg I have edited.But 1st one works fine for me every time .
Yes, it can be successfully compiled but after running it, it get segmentation fault: len p = 7 15125 Segmentation fault: 11
Well i see that your array is having 7 elements and you are accessing s[][7] that will be invalid because in c index start from 0
Could you please tell me where do I access s[ ][7]? In the code, len = 7, but I pass len-1 to the function findtrace as j. Since the maximum of j is len-1 = 6, so I am still a little confulsed
|
0

Problem seems to be in recursive function : Some sort of Access Volition because of some logical mistake

variable i saves the vales -858993460 so when it comes to printf("%d\t",s[i][j]); it gives access violation because such an index doesn't exist

another problem is const int len = sizeof(p)/sizeof(int); instead of using simple int,

a little bit refined form is here , but logic still need to be fixed

void findtrace(int i, int j, int s[][7])
{
    if(i==j)
        printf("%d\t", i);
    else{
        printf("%d\t",s[i][j]);
        findtrace(i,s[i][j],s);
        findtrace(s[i+1][j],j,s);
    }
}

int main(){
    int p[] = {30,35,15,5,10,20,25};
    const int len = sizeof(p)/sizeof(int);
    //void findtrace(int[][len]s, int i, int j);
    int m[len][len];
    int s[len][len];
    printf("len p = %d\n",len);
    for(int i=1;i<=len;i++)
        m[i][i] = 0;
  //  int temp;
    for(int k=1;k<len;++k){
        for(int j=k+1;j<len;++j){
            int i = j-k;
            m[i][j] = m[i][i]+m[i+1][j]+p[i]*p[i-1]*p[j];
            s[i][j] = i;
            for(int t=i+1;t<j;++t){
                if( m[i][t]+m[t+1][j]+p[i-1]*p[j]*p[t]<m[i][j] )
                m[i][j] = m[i][t]+m[t+1][j]+p[i-1]*p[j]*p[t];
                s[i][j] = t;
            }
            //printf("m[%d][%d] = %d\t",i,j,m[i][j]);
        }
    }
    printf("\n%d\n",m[1][len-1]);
    findtrace(1,len-1,s);
}
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1 Comment

Thanks, the problem is indeed because of the recursion.

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