I want to code a basic interpreter / scripting language. Like

Yes, here is tons of resources about compiler design. SICP includes a whole chapter about it iirc. A basic google search give a tutorial and an online textbook.

OP here

for instance my program input before converted to opcodes would be:

line 1 - STORE 349 (ie store a value here)
line 2 - INCR 1 (increment adress 1 by 1)
line 3 - PRINT 1 (print what is at adress 1)
line 4 - GOTO 2

I don't know if it's possible to make it work if all opcodes should fit on 1 line (ie 32 bits) and each line can also store a value

But I don't want to have variable opcodes and complex stuff, I just want to be able to iterate on memory locations of the same size

Are you retarded? You are basically asking "how do I read data from a file?" Also why would you use a 32 bit opcode? I bet 256 ops aka 8 bits is just fine.

#define OP_HALT 0
#define OP_INC 1
#define OP_OUT 2

#define CHUNK 256

typedef struct {
  uint8_t *code;

  uint32_t ip;
  uint32_t register;
  uint8_t halt;
} mach;

int execfile(const char *file, mach *m) {
  m->code = malloc(CHUNK);
  if (code == NULL) return 1;

  int fd = open(file, O_RDONLY);
  if (fd == -1) {
    free(m->code);
    return 1;
  }

 // TODO roll your own memory management for dynamic allocs
  read(fd, m->code, CHUNK);

  // Exec code until halt
  while (execop(m)) {}

  free(m->code);
  return 0;
}

int execop(mach *m) {
  // Is machine halted?
  if (m->halt) return 1;

  uint8_t op;
  op = m->code[m->ip];
  m->ip++;

  // One byte ops
  switch(op) {
    case OP_HLT:
      m->halt = 1;
      return 0;
   case OP_OUT:
      printf("Register: %i\n", m->register);
      return 0;
  }

  uint32_t arg;
  // Ops with arg
  arg = (uint32_t) m->code[m->ip];
  m->ip += 4;

  switch (op) {
    case OP_INC:
       mach->register += arg;
       return 0;
    default:
      // Invalid opcode
      return 1;
  }
}

And no, I didn't test it, I just wrote it in 5 minutes.