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Output of C programs | Set 56 (While loop)

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Prerequisite : While loops Q.1 What is the output of this program?
#include <iostream>
using namespace std;
int main()
{
    unsigned int x = 3;
    while (x-- >= 0) {
        printf("%d  ", x);
    }
    return 0;
}

                    
Option a) 3 2 1 0 b) 2 1 0 -1 c) infinite loop d) -65535
Answer : C
Explanation: Here x is an unsigned integer andit can never become negative. So the expression x–>=0 will always be true, so its a infinite loop. Q.2 What is the output of this program?
#include <iostream>
using namespace std;
int main()
{
    int x = 3, k;
    while (x-- >= 0) {
        printf("%d  ", x);
    }
    return 0;
}

                    
option:- a a) 3 2 1 0 b) 2 1 0 -1 c) infinite loop d) -65535
Answer: b 
Explanation: Here x is an integer with value 3. Loop runs till x>=0 ; 2, 1, 0 will be printed and after x>=0, condition becomes true again and print -1 after false. Q.3 What is the output of this program?
#include <iostream>
using namespace std;
int main()
{
    int x = 0, k;
    while (+(+x--) != 0) {
        x++;
    }
    printf("%d  ", x);
    return 0;
}

                    
option a) 1 b) 0 c) -1 d) infinite
Answer : C 
Explanation Unary + is the only dummy operator in c++. So it has no effect on the expression. Q.4 What is the output of this program?
#include <iostream>
using namespace std;
int main()
{
    int x = -10;
    while (x++ != 0)
        ;
    printf("%d  ", x);
    return 0;
}

                    
option a) 0 b) 1 c) -1 d) infinite
Answer: b 
Explanation: The semicolon is after the while loop. while the value of x become 0, it comes out of while loop. Due to post-increment on x the value of x while printing becomes 1. Q.5 What is the output of this program?
#include <iostream>
using namespace std;
int main()
{
    while (1) {
        if (printf("%d", printf("%d")))
            break;
        else
            continue;
    }
    return 0;
}

                    
option a) Garbage value b) 1 c) 0 d) Error
Answer : a 
Explanation: The inner printf executes and print some garbage value.

Last Updated : 25 Sep, 2017
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