CODEWITHSUNDEEP
carrays
Malo Polsky
Malo Polsky

Reputation: 47

Arrays with C - What are those numbers?

I created this small piece of software in C:

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

void print_this_list(int size){
    int list[size];
    for (int i = 0; i < size; i++) {
        printf("%d\n", list[i]);
    }
}

int main(int argc, char *argv[]){

    print_this_list(25);
    return 0;

}

The results of the execution are very interesting (apparently) random numbers:

-1519340623
859152199
-1231562870
-1980115833
-1061748797
1291895270
1606416552
32767
15
0
1
0
104
1
1606578608
32767
1606416304
32767
1606423158
32767
1606416336
32767
1606416336
32767
1
Program ended with exit code: 0

What exactly are those numbers and what is the "logic" behind them?

Upvotes: 0

Views: 103

Answers (2)

ameyCU
ameyCU

Reputation: 16607

No logic behind them .It's Undefined Behaviour 

void print_this_list(int size){
int list[size];             // not initialized 
for (int i = 0; i < size; i++) {
    printf("%d\n", list[i]);             // still you access it and print it 
  }
}

list is uninitialized and you print it's contents (which are indeterminate) .Therefore ,you get some random garbage values as output.

In order to get working you need to initialize it . You can try this -

  void print_this_list(int size){
  int list[size];             
  for (int i = 0; i < size; i++) {
    list[i]=i;                 // storing value of i in it before printing        
    printf("%d\n", list[i]);             
    }
  }

Upvotes: 9

Anas Shami
Anas Shami

Reputation: 1

it's trash . uninitialized value

if you try 

    int x; // i define x as uninitialized variable some where in the memory (non empty)
    printf("%d",x); // will print trash "unexpected value  
    // if i do this 
    int x=10;//i define x with initial value so i write over the trash was found in this block of the memory .

and if i print out of range index as 

  int ar[10];
  for(int i=0;i<10;i++)
      ar[i]=rand();
  printf("%d\n",ar[10]);//out of index uninitialized index it will print trash .

i hope that's help

Upvotes: 0

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