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Monday 1 March 2010

C Question of the Day -Preprocessor

1.What is the output of the following program?
#include<stdio.h>
#define PRODUCT(x) (x*x)
int main()
{
    int a=4,z;
    z=PRODUCT(a+1);
    printf("z=%d\n",z);
    return 0;
}
Solution


z=9
The expected output is 25. But the preprocessor replaces z=PRODUCT(4+1) as z=(4+1*4+1).* has higher preceddence than + . so the output is 4+4+1=>z=9

2.What is the output of the following program?
#include<stdio.h>
#define PRODUCT(x) (x*x)
int main()
{
    int a=4,x,y;
    x=PRODUCT(a++);
    y=PRODUCT(++a);
    printf("X=%d\t Y=%d\n",x,y);
    return 0;
}
Solution
X=16 Y=64


3.What is the output of the following program?
#include<stdio.h>
#define SEMI ;
int main()
{
    int x=4 SEMI ;
    printf("X=%d\n",x)SEMI
    return 0 SEMI
}
Solution
x=4
The program will not produce error.C statements should end with a semicolon. The compiler will take the 2nd  ; as a empty statement in line 5.


4.What is the output of the following program?
#include<stdio.h>
#define CHAR1 char
int main()
{
    typedef char CHAR2;
    CHAR1 x;
    CHAR2 y;
    x=255;
    y=255;
    printf("X=%d\tY=%d\n",x,y);
    return 0;
}
Solution
X=-1 Y=-1
default value of char is signed char.so the value above 127 are taken as the 2's complement value


5.What is the output of the following program?
#include<stdio.h>
#define SIZE sizeof(int)
int main()
{
    int i=-1;
    if(i<SIZE)
        printf("True\n");
    else
        printf("False\n");
    return 0;
}
Solution
False


6.What is the output of the following program?
#include<stdio.h>
#define SIZE(a) (&a+1) - &a
int main()
{
    float x;
    printf("X=%d\n",SIZE(x));
    return 0;
}
Solution
X=1

4 comments:

  1. I cant understand the solution to the 2nd one. Any help??

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  2. //for the 2nd problem
    Consider the 2nd program with added printf statements
    #include
    #define PRODUCT(x) (x*x)
    int main()
    {
    int a=4,x,y;
    x=PRODUCT(a++);
    printf("a=%d\n",a);
    y=PRODUCT(++a);
    printf("a=%d\n",a);
    printf("X=%d\t Y=%d\n",x,y);
    return 0;
    }
    the output of the above program is ./a.out
    a=6
    a=8
    X=16 Y=64
    The Preprocessed file is given below
    int main()
    {
    int a=4,x,y;
    x=(a++*a++);
    printf("a=%d\n",a);
    y=(++a*++a);
    printf("a=%d\n",a);
    printf("X=%d\t Y=%d\n",x,y);
    return 0;
    }
    initially a value is 4
    x=(a++*a++);-----> a++ will assign a first then only increment the value so x=a*a=4*4=16 after that 4++ will give 5 and again a++=>5++=>6
    So before the statement y=PRODUCT(++a); a value is 6. now y=(++a*++a); In this ++a will first increment the value of a and then assign the value. already a value is 6. So the first ++a=>++6 will incrment a to 7 and next ++a will increment 7 to 8. now a*a=8*8=64
    y value is 64.

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  3. thanks for programming
    from gaurav and sameer

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