C Programming - C Preprocessor
#include<stdio.h>
#define PRINT(int) printf("int=%d, ", int);
int main()
{
int x=2, y=3, z=4;
PRINT(x);
PRINT(y);
PRINT(z);
return 0;
}
The macro PRINT(int) print("%d,", int); prints the given variable value in an integer format.
Step 1: int x=2, y=3, z=4; The variable x, y, z are declared as an integer type and initialized to 2, 3, 4 respectively.
Step 2: PRINT(x); becomes printf("int=%d,",x). Hence it prints 'int=2'.
Step 3: PRINT(y); becomes printf("int=%d,",y). Hence it prints 'int=3'.
Step 4: PRINT(z); becomes printf("int=%d,",z). Hence it prints 'int=4'.
Hence the output of the program is int=2, int=3, int=4.
#include<stdio.h>
#define SWAP(a, b) int t; t=a, a=b, b=t;
int main()
{
int a=10, b=12;
SWAP(a, b);
printf("a = %d, b = %d\n", a, b);
return 0;
}
The macro SWAP(a, b) int t; t=a, a=b, b=t; swaps the value of the given two variable.
Step 1: int a=10, b=12; The variable a and b are declared as an integer type and initialized to 10, 12 respectively.
Step 2: SWAP(a, b);. Here the macro is substituted and it swaps the value to variable a and b.
Hence the output of the program is 12, 10.
#include<stdio.h>
#define FUN(i, j) i##j
int main()
{
int va1=10;
int va12=20;
printf("%d\n", FUN(va1, 2));
return 0;
}
The following program will make you understand about ## (macro concatenation) operator clearly.
#include<stdio.h>
#define FUN(i, j) i##j
int main()
{
int First = 10;
int Second = 20;
char FirstSecond[] = "IndiaBIX";
printf("%s\n", FUN(First, Second) );
return 0;
}
Output:
-------
IndiaBIX
The preprocessor will replace FUN(First, Second) as FirstSecond.
Therefore, the printf("%s\n", FUN(First, Second) ); statement will become as printf("%s\n", FirstSecond );
Hence it prints IndiaBIX as output.
Like the same, the line printf("%d\n", FUN(va1, 2)); given in the above question will become as printf("%d\n", va12 );.
Therefore, it prints 20 as output.
#include<stdio.h>
#define FUN(arg) do\
{\
if(arg)\
printf("IndiaBIX...", "\n");\
}while(--i)
int main()
{
int i=2;
FUN(i<3);
return 0;
}
The macro FUN(arg) prints the statement "IndiaBIX..." untill the while condition is satisfied.
Step 1: int i=2; The variable i is declared as an integer type and initialized to 2.
Step 2: FUN(i<3); becomes,
do
{
if(2 < 3)
printf("IndiaBIX...", "\n");
}while(--2)
After the 2 while loops the value of i becomes '0'(zero). Hence the while loop breaks.
Hence the output of the program is "IndiaBIX... IndiaBIX..."
#include<stdio.h>
#define MAX(a, b) (a > b ? a : b)
int main()
{
int x;
x = MAX(3+2, 2+7);
printf("%d\n", x);
return 0;
}
The macro MAX(a, b) (a > b ? a : b) returns the biggest value of the given two numbers.
Step 1 : int x; The variable x is declared as an integer type.
Step 2 : x = MAX(3+2, 2+7); becomes,
=> x = (3+2 > 2+7 ? 3+2 : 2+7)
=> x = (5 > 9 ? 5 : 9)
=> x = 9
Step 3 : printf("%d\n", x); It prints the value of variable x.
Hence the output of the program is 9.