Q:

Making a variable accessible by other functions in C

I'm new to programming and we just learned arrays in class. 
We are tasked to create a C program without using global variables.  
I created two functions, one for inputting the data and one for the operations (containing a menu).  After making the user choose which operation he would like to do in the operations menu, it will display the result and return back to the menu.  
I couldn't figure out how to make some of the variables readable by the operations function since we are not allowed to use global variables. 
void matrix(){
int a, b, c, d, k, m, n, p, q, s=0, first[MAX][MAX], second[MAX][MAX], msum[MAX][MAX], firstt[MAX][MAX], secondt[MAX][MAX], prod[MAX][MAX];
system("CLS");
printf("/-----------------------------------------------------------------------------/\n"
       "\t\t\t\tMatrix\n"
       "/-----------------------------------------------------------------------------/\n");
printf("This program will multiply matrices (up to 3x3 matrix only).\n"
       "Please enter the number of rows of the first matrix: ");
scanf("%d", &m);
if(m>3){
    matrixerror();
}
printf("Please enter then number of columns of the first matrix: ");
scanf("%d", &n);
if(n>3){
    matrixerror();
}
printf("Please enter the number of rows of the second matrix: ");//Matrix 2
scanf("%d", &p);
if(p>3){
    matrixerror();
}
printf("Please enter then number of columns of the second matrix: ");
scanf("%d", &q);
if(q>3){
    matrixerror();
}
printf("\nPlease enter the elements of the first matrix:\n");
for(c=0; c<m; ++c)
    for(d=0; d<n; ++d){
        printf("Enter element a%d%d: ",c+1, d+1);
        scanf("%d", &first[c][d]);
    }
printf("\nPlease enter the elements of the second matrix:\n");   
for(c=0; c<p; ++c)
    for(d=0; d<q; ++d){
        printf("Enter element b%d%d: ",c+1, d+1);   
        scanf("%d", &second[c][d]);
    }

matrixmenu();
}

and the other one for the operations 
void matrixmenu(){
system("CLS");
char choice;
printf("/-----------------------------------------------------------------------------/\n"
       "\t\t\t\tMatrix\n"
       "/-----------------------------------------------------------------------------/\n");

printf("\n"
       "\t1.   Add Matrices\n"
       "\t2.   Multiply Matrices\n"
       "\t3.   Transpose \n"
       "\tB.  Back \n");
printf("\n\tFirst matrix is : \n\t");
for(a=0; a<m; ++a)
    for(b=0; b<n; ++b){
        printf("%d  ", first[a][b]);
        if (b == n-1)
        printf("\n\n\t");
    }
printf("\n\tSecond matrix is : \n\t");
for(a=0; a<m; ++a)
    for(b=0; b<n; ++b){
        printf("%d  ", second[a][b]);
        if (b == n-1)
        printf("\n\n\t");
    }      
printf("\n");   
printf("/------------------------------------------------------------------------------/ ");
scanf("%s", &choice);
switch(choice){
    case '1':
        printf("\n\tThe sum of entered matrices is: \n\t");

        for (a = 0; a < m; a++){
            for (b = 0 ; b < n; b++){
                msum[a][b] = first[a][b] + second[a][b];
                printf("%d\t", msum[a][b]);
            }
            printf("\n\t");
        }
        printf("\n\t");
        system("PAUSE");
        matrixmenu();
        break;
    case '2':
        if (n ! = p){
            printf("\n\tError!  Matrix cannot be multiplied!\n\t");
            system("PAUSE");
            matrixmenu();
        }
        for (c = 0; c < m; c++){
            for (d = 0; d < q; d++){
                for (k = 0; k < p; k++){
                    s = s + first[c][k]*second[k][d];
                }
            prod[c][d] = s;
            s = 0;
            }
        }
        printf("\n\tThe product matrix is:\n\t");
        for (c = 0; c < m; c++){
            for (d = 0; d < q; d++){
                printf("%d\t", prod[c][d]);
            }
            printf("\n\t");
        }   
        printf("\n\t");
        system("PAUSE");
        matrixmenu();
        break;
    case '3':
        for(a=0; a<m; ++a)//Tranposition
            for(b=0; b<n; ++b)
                firstt[b][a] = first[a][b];
        printf("\n\tThe transpose of the first matrix is:\n\t");
        for(a=0; a<n; ++a)
            for(b=0; b<m; ++b){
                printf("%d  ",firstt[a][b]);
            if(b==m-1)
            used    printf("\n\n\t");
        }
        for(a=0; a<p; ++a)//Tranposition
            for(b=0; b<q; ++b)
                secondt[b][a] = second[a][b];
        printf("\n\tThe transpose of the second matrix is:\n\t");
        for(a=0; a<n; ++a)
            for(b=0; b<m; ++b){
                printf("%d  ",secondt[a][b]);
            if(b==m-1)
                printf("\n\n\t");
            }   
        printf("\n\t");
        system("PAUSE");
        matrixmenu();
        break;
    case 'B':
    case 'b':
        mainmenu();
        break;
    default:
        matrixmenu();
        break;
}
}

A:

You Can Pass Address of variable to function in which you want to work with that variable . 
Let us take an example , suppose 
#include<stdio.h>

void testing(int *);

int main(){

  int  x = 3;
  printf("%d\n" , x);

  testing(&x);
  printf("%d" , x);

   }

  void testing(int *j){
     *j = 8;
   }

Output Would Be 3 8 , now x is changed in caller function because you passed the address of x (&x) to the function testing and by using *j you are dereferencing that address and storing 8 in the address that j is pointing to , so in effect x changes because you stored its address in a pointer that now points to that address and then you passed that address to other function and where you dereferenced that address (Dereferencing a pointer means getting the value that is stored in the memory location pointed by the pointer.  The operator * is used to do this, and is called the dereferencing operator) and changed the value that is stored .  
For More Information Look At This Question What does "dereferencing" a pointer mean?