Thread: I need help with my code, i really dont know thats wrong with it

The code works perfectly if for example if i want to check 3 quadrilaterals, but when i want to check 5 quadrilateralsit almost always prints the first wrong and the rest just fine, and i dont know why that is or how to fix it.

Code:

#include <stdio.h>
#include <stdlib.h>

int main()
{
  int check;
  int i = 1;
  int a[i];
  int b[i];
  int c[i];
  int d[i];
 
  
  
  
  printf("Please enter the number of quadrilaterals to check: ");
  scanf("%d", &check);
  if(!(check >= 1) || !(check <=127))
  {
    while(!(check >= 1) || !(check <=127))
    {
      printf("Error: Invalid number of quadrilaterals.\n");
      printf("Please enter the number of quadrilaterals to check: ");
      scanf("%d", &check);
    }
  }
 
  


  while(i <= check){
  printf("Please enter the four sides for quadrilateral %d: ", i);
  scanf("%d" "%d" "%d" "%d", &a[i], &b[i], &c[i], &d[i]); 
  if((!(a[i] >= 1) || !(a[i] <= 225)) || (!(b[i] >= 1) || !(b[i] <= 225)) || (!(c[i] >= 1) || !(c[i] <= 225)) || (!(d[i] >= 1) || !(d[i] <= 225))) 
  {
    while((!(a[i] >= 1) || !(a[i] <= 225)) || (!(b[i] >= 1) || !(b[i] <= 225)) || (!(c[i] >= 1) || !(c[i] <= 225)) || (!(d[i] >= 1) || !(d[i] <= 225)))
    {
      printf("Error: Invalid number of side.\n");
      printf("Please enter the four sides for quadrilateral %d: ", i);
      scanf("%d" "%d" "%d" "%d", &a[i], &b[i], &c[i], &d[i]);
    }
  }    
    
  i++;
  
}
  for(i = 1; i <= check; i++) {
    if(a[i] == b[i] && a[i] == c[i] && a[i] == d[i]){
      printf("Quadrilateral %d : (a= %d,  b= %d, c= %d, d= %d) is square.\n", i, a[i], b[i], c[i], d[i]);
    }
    else if (a[i] == c[i] && b[i] == d[i]){
      printf("Quadrilateral %d : (a= %d,  b= %d, c= %d, d= %d) is rectangle.\n", i, a[i], b[i], c[i], d[i]);
    }
    else if ((a[i] == c[i] && b[i] != d[i]) || (a[i] != c[i] && b[i] == d[i])){
      printf("Quadrilateral %d : (a= %d,  b= %d, c= %d, d= %d) is isosceles trapezium.\n", i, a[i], b[i], c[i], d[i]);
    }
    else if ((a[i] == d[i] && b[i] == c[i]) || (a[i] == b[i] && c[i] == d[i])){
      printf("Quadrilateral %d : (a= %d,  b= %d, c= %d, d= %d) is kite.\n", i, a[i], b[i], c[i], d[i]);
    }
    else printf("Quadrilateral %d : (a= %d,  b= %d, c= %d, d= %d) is irregular quadrilateral.\n", i, a[i], b[i], c[i], d[i]);
      
      
  
    
    }

  
  
  
  
  return 0;
  
}

> int i = 1;
> int a[i];
You don't create a[2] just by doing i++ later on in the code.

What you do end up doing is trashing memory.

If you want 5, then create 5 up front.

Well
int a[128];
etc is no big deal on a modern machine.

Code:

// clockwise 

#include <stdio.h>

void typeOfQuad(int a, int b, int c, int d) {
    if (a == b && b == c && c == d && d == a) {
        printf("square");
    }
    if (a == c && b == d) printf("rectangle");
    //etc...
}

int main() {

    int quads;
    printf("Enter the number of quadrilaterals to check: ");
    scanf("%d",&quads); 
    int a[quads], b[quads], c[quads], d[quads];

    for (int i = 1; i < (quads+1); i++) {
        printf("Enter the four sides of quadrilateral %i: ", i);
        scanf("%d %d %d %d", &a[i-1], &b[i-1], &c[i-1], &d[i-1]);
        printf("\n");
    }

    for (int i = 0; i < quads; i++) {
        printf("Quadrilateral %d is ", i );
            typeOfQuad( a[i], b[i], c[i], d[i] );
        printf(".\n");
    }

    return 0;
}