error: no match for ‘operator[]’

[Kiran Sagar]

hi everyone,
i have written a code in c++. first i created a structure "elements". then declared a array "m" of datatype "elements" in the main(). When i passed this variable to a function by reference, i got this error

tdma.cpp:7:12: error: no match for ‘operator[]’

i got the same error for many lines within the function
below is the code which i am working on.

#include<iostream>
struct elements
{ float a,b,d,p,f,q;
};
int tdma(struct elements m)
{ int n=0;
while(m[n].a!='\0') // here is the error- m[n].a
{ n++;}
m[0].p=-(m[0].b)/(m[0].d);
m[0].q=m[0].f/m[0].d;
for(int i=1;i<n;i++)
{ m[i].p=-m[i].b/(m[i].d+m[i].a*m[i-1].p);
m[i].q=(m[i].f-m[i].a*m[i-1].q)/(m[i].d+m[i].a*m[i-1].p);
}
m[n-1].p=0;
return 0;
};
int main()
{ using namespace std;
float tdm[4][4]; elements m[4];
int n=4;

for(int i=0;i<n;i++)
{ tdm[i][i]=-2;
for(int j=1;j<n;j++)
{ if((i-j)*(i-j)==1)
tdm[i][j]==1;
}
}
m[0].a=2;
cout<<m[0].a;
return 0;
}

please tell me what's going wrong. thanks in advance

[Moschops]

int tdma(struct elements m)
Inside the function tdma, m is not an array. It is a single elements object.

If you want to pass in an array, try
int tdma(elements* m)

I see that in your code you never actually call the function tdma. If you aren't using it, you can just delete it.

[Kiran Sagar]

forgot to tell you, the program is not complete. there may be other irrelevant mistakes in the program, please dont care about that and just help me with the error.

[Kiran Sagar]

thanks Moschops for the help, i dont see the error now after the modification you suggested. just one more thing, if i want to pass it by reference then can i try

int tdma(elements* &m)

[1vRz3TCk]

int tdma(elements (&m)[4])
{...}

Here, m is a reference to an array of 4 elements

[Moschops]

You can pass the array by reference, but there's very little point in doing that. When you pass an array, you actually pass a pointer to that array, so any changes you make persist when the function returns.

[1vRz3TCk]

When you pass a pointer to an array you would also need to pass the dimensions of the array.

[Kiran Sagar]

thanks for the help

[Moschops]

When you pass a pointer to an array you would also need to pass the dimensions of the array.

I disagree. I regularly pass just a pointer to an array. It's common practice. strcpy springs to mind as a commonly used function in which just a pointer to the array is passed.

[1vRz3TCk]

Moschops wrote:

I regularly pass just a pointer to an array. It's common practice.

I never said otherwise. I also regularly pass pointer to arrays (along with the dimensions of the array). Char arrays are a bit different because they use a null character to terminate the string but on the whole you need a method of knowing how big the array is.