Uninitialized Primitive Data Types in C/C++

In this section we will see when we declare one variable that is un-initialized, which value they hold in C or C++ language. Sometimes we assume that the compiler assigns some value like 0 for int, 0.0 for float etc. But what will be for character datatype? Let us see using implementation and compile using different compilers.

Example (C++)

Let us see the following implementation to get better understanding −

 Live Demo

#include <iostream>
using namespace std;
int main() {
   char char_var;
   float float_var;
   int int_var;
   double double_var;
   long long_var;
   cout << char_var << endl;
   cout << float_var << endl;
   cout << int_var << endl;
   cout << double_var << endl;
   cout << long_var << endl;
}

Output (Compiled in Cpp.sh)

0
0
0
0

Output (Compiled in Online GDB)

5.88054e-39
0
6.95297e-310
0

Output (Local System)

9.73438e-039
4309744
1.15685e-306
-53505136

Now the question comes why C/C++ compiler does not initialize variables with default values? The answer is simple, the overhead of initializing a stack variable is expensive as it hampers the speed of execution, as a result of this these variables can consist of indeterminate values. So, it is treated as good practice to initialize a primitive data type variable before applying it in code.