Undeclared first use of function

It gave me the undeclared first use of function:

Code:

#include <iostream>
#include <stdio.h>
#include <string>
using namespace std;

#define max_size = 100;

int main ()
{

    //float instrs[max_size];
 FILE * fin;
 fin = fopen("test.txt", "r");
unsigned int oneinst;
int i;

while (!feof(fin))
      {
    fscanf(fin, "%x", &oneinst);
    int    instrs[] = {oneinst};
      }

for(int i = 0; i < 5; i++)

        {

        int opcode = (instrs[i] >> 26) & 0x3F;
           }  
 

    return 0;
}

For reason when I run this I get the error: `instrs' undeclared (first use this function)

If you indented the code properly, the reason might become apparent:

Code:

#include <iostream>
#include <stdio.h>
#include <string>
using namespace std;

#define max_size = 100;

int main()
{
    //float instrs[max_size];
    FILE* fin;
    fin = fopen("test.txt", "r");
    unsigned int oneinst;
    int i;

    while (!feof(fin))
    {
        fscanf(fin, "%x", &oneinst);
        int instrs[] = {oneinst};
    }

    for (int i = 0; i < 5; i++)
    {
        int opcode = (instrs[i] >> 26) & 0x3F;
    }

    return 0;
}

As you can see, instrs is local to the while loop, so it does not exist in the for loop. You should have declared it before the loops by uncommenting:

Code:

float instrs[max_size];

Though it looks like instrs should be an array of int, not float. Also, this would then be wrong:

Code:

#define max_size = 100;

You could have written:

Code:

const int max_size = 100;

You should not use feof to control a loop like that (why not just use C++-style I/O?), and then you need to make other changes to get your program to work.

Thank you very much laserlight, you have been more than helpful

Originally Posted by TheXx11

what is this C++ I/O style, what do I need to google search to find out more about it?

You already #include <iostream>. Search for that.