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C Preprocessor - Programming

Q1:

What will be the output of the program? 
#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;
}

A a = 10, b = 12

B a = 12, b = 10

C Error: Declaration not allowed in macro

D Error: Undefined symbol 't'

ANS:B - a = 12, b = 10

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.