如果Printf在函数中，则C ++返回是不同的

Question

I am experiencing a rather strange thing. I am currently working on a function that calculates the shape factor of a shape. The perimeter and area functions work perfectly fine however I have discovered something.

The code that out puts the right answer

double Shapefactor (char line [50][50]){

double sfactor;
double perimeter1= (Perimeter(line));
printf("peri = %f", perimeter1);
double area1=((double)Area(line));
sfactor = ((perimeter1 * perimeter1) /area1);                           
printf("----------------------------------------------------*Therefore the shape factor for the given shape is* %f \n", sfactor);  

   return (sfactor);                                              
 }

This provides me the correct output. However if I was to remove this line from the code

printf("peri = %f", perimeter1);

Then it gives me the wrong number. Do you have any idea why this is?

Area code

int Area (char line [50][50]){
int x;                                                       
int y;
int sum;                                                       

  for (x = 0; x <= 50; x++) {                                
    for (y = 0; y <= 50; y++) {                              


      if (line[x][y] == '1')                                 
        sum++;                                           

    }
  }



 return (sum);                                                  

 }

Perimeter

int Perimeter (char line [50][50]){
int x;                                                      
int y;
int sumup;                                                       
FILE * f_ptr;
char filename[20];


  for (x = 0; x < 50; x++) {
    for (y = 0; y < 50; y++) {

      if (line[x][y + 1] == '0' & line[x][y] == '1')         
        sumup++;                                                    
      else if (line[x][y] == '1' & line[x][y - 1] == '0')  
        sumup++;                                                   
      else if (line[x + 1][y] == '0' & line[x][y] == '1')    
        sumup++;                                                  
      else if (line[x][y] == '1' & line[x - 1][y] == '0')   
        sumup++;                                                   

    }
  }

 return (sumup);                                                    

  }

Thank you

Answer 1

The variable sum in Area() (EDIT: and also sumup in Perimeter() , as noted by @agbinfo) is uninitialized:

int Area (char line [50][50]){
//...
int sum;                                                       

  for (x = 0; x <= 50; x++) {
    for (y = 0; y <= 50; y++) {
      if (line[x][y] == '1')
        sum++;
//...

This is undefined behavior; this being an automatic variable, it's likely what you're reading there is garbage left on the stack by a previous function call, ie whether you invoke printf() or not makes the difference you're seeing.

I recommend enabling compiler warnings and linters which would usually catch these sort of errors.