Multidimensional Array does not hold values

Question

I have been trying to see where the problem is but couldnt find it. Every time, the values of array memory gives me 0, even though int count works and keeps counting as the struct data value, only array does not save the value.

#include<stdlib.h>
#include<stdio.h>
#define SIZE 1000

struct registers
 {
   int data;     
 } registerX;

void first(int *counter, struct registers* X1, int m[][2])
{
 int value;
 printf("Enter the value for the X\n");
 scanf("%d", &value);
 X1->data = value;
 m[*counter][1] = X1->data;
 *counter = ++*counter;   
}


int main()
{
int memory[SIZE][2];
int choice;
int count = 0;
printf("Enter the instruction number:\n");

while(choice != 107)

 {

   scanf("%d", &choice);
   if(choice == 101)
   {
       memory[count][0] = 101;
       first(&count, &registerX, memory);
       printf("%d\n", memory[count][1]);
        printf("%d\n", memory[count][0]);
   } 
  }
}

Duplicate. `*counter = ++*counter;` has undefined behaviour. (E.g. see http://stackoverflow.com/q/4176328/596781, https://stackoverflow.com/questions/949433/why-are-these-constructs-using-undefined-behavior.) — Kerrek SB, Nov 29 '14 at 15:36

score 1 · Answer 1 · answered Nov 29 '14 at 16:16

You have some problems in your code.

Firstly,choice in while(choice != 107) is uninitialized. To fix it,use a do...while loop instead of a while loop as you want the loop body to execute once before checking the condition.

Secondly,*counter = ++*counter; undefined behaviour has KerrekSB points out in his comment. To fix it,use (*counter)++;.

Lastly,you print uninitialized elements of your array in the last two printfs. The reason is that you increment *counter in the function which will also modify count in main as counter is a pointer which points to the address of count.

Multidimensional Array does not hold values

1 Answers1