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C Program to Redeclaration of global variable
We will understand how C and C++ behave differently in case we re-declare a global variable without initializing, redeclaring global variables with initialization, redeclaring global variables and initializing them twice. Also, we will repeat above combinations with local variables.
1. A) C program : Redeclaring Global variables with no initialization
#include <stdio.h>
int var;
int var;
int main(){
printf("Var = %d",var);
return 0;
}Output
Var = 0
B) C++ program : Redeclaring Global variables with no initialization
#include <iostream>
using namespace std;
int var;
int var;
int main(){
cout<<"Var = "<<var;
return 0;
}Output
Compilation Error: int var; main.cpp:3:5: note: ‘int var’ previously declared here
Results:- C allows redeclaration of global variables without initialization. Value remains 0. C++ gives a Compilation error that the variable is redeclared.
2. A) C program : Redeclaring Local variables with no initializations
#include <stdio.h>
#include <stdio.h>
int main(){
int var;
int var;
printf("Var = %d",var);
return 0;
}Output
error: redeclaration of ‘var’ with no linkage
B) C++ program : Redeclaring Local variables with no initialization
#include <iostream>
using namespace std;
int main(){
int var;
int var;
cout<<"Var = "<<var;
return 0;
}Output
error: redeclaration of ‘int var’
Results:- Both C and C++ do not allow redeclaration of local variables with no initialization done. Both programs failed in compilation.
3. A) C program : Redeclaring Global variables with initialization
#include <stdio.h>
int main(){
int var;
int var=10;
printf("Var = %d",var);
return 0;
}Output
Var = 10
B) C++ program : Redeclaring Global variables with initialization
#include <iostream>
using namespace std;
int var;
int var=10;
int main(){
cout<<"Var = "<<var;
return 0;
}Output
main.cpp:7:9: error: redeclaration of ‘int var’ int var;
Results:-C allows redeclaration of Global variable if it is uninitialized. C++ program fails during compilation.
4. A) C program : Redeclaring Global variables with initialization
#include <stdio.h>
int var;
int var=10;
int main(){
printf("Var = %d",var);
return 0;
}Output
error: redeclaration of ‘var’ with no linkage
B) C++ program : Redeclaring Local variables with initialization
#include <iostream>
using namespace std;
int main(){
int var;
int var=10;
cout<<"Var = "<<var;
return 0;
}Output
error: redeclaration of ‘int var
Results:-Both C and C++ do not allow redeclaration of local variables even if it is uninitialized. Both programs failed in compilation
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