Control Instructions Questions and Answers

Q: Output? #include <stdio.h> int main() { int c = 5, no = 10; do { no /= c; } while(c--); printf ("%d\n", no); return 0; }

Correct answer: Runtime ErrorThe loop divides no by c and then tests c--, so c falls 5, 4, 3, 2, 1, 0. On the pass after the test that saw c equal to 1, c is 0 - and no /= 0 is integer division by zero, which the hardware traps. The compiler cannot see it, so it is a run-time fault.

Q: What is the output of the below program? #include <stdio.h> int main() { int i = 0; switch (i) { case '0': printf("Geeks"); break; case '1': printf("Quiz"); break; default: printf("GeeksQuiz"); } return 0; }

Correct answer: GeeksQuiz'0' is a character constant, and its value is the ASCII code 48, not the number 0. Likewise '1' is 49. The controlling expression is 0, which matches neither, so control falls to default.

Q: When 2 is entered, The output of the code below is? #include <stdio.h> void main() { int ch; printf("enter a value btw 1 to 2:"); scanf("%d", &ch); switch (ch) { case 1: printf("1\n"); break; printf("Hi"); default: printf("2\n"); } }

Correct answer: 2ch is 2, which matches no case, so control goes straight to default and prints 2. The printf("Hi") is unreachable in any event: it sits immediately after a break and before the next label, so no path can reach it.

Q: Which of the following cannot be used as LHS of the expression in for (exp1;exp2; exp3) ?

Correct answer: macrosThe three parts of a for are ordinary expressions, so anything assignable can appear on the left of an assignment in them - a variable, or the result of a function returning a modifiable lvalue. A macro is only text, replaced before compilation, so what appears in the code is whatever it expands to; it is not itself an object and cannot be assigned to.

Q: The following code ‘for(;;)’ represents an infinite loop. Which statement exits the loop itself?

Correct answer: breakbreak is the statement that ends the loop: control passes to the statement after it and the program carries on. exit(0) and abort() would also stop the loop running, but only by ending the whole program, which is a different thing from leaving the loop.

Q: Which keyword is used to come out of a loop only for that iteration?

Correct answer: continuecontinue abandons the current iteration and jumps to the next one - to the update expression in a for, or to the condition test in a while. break leaves the loop altogether, and return leaves the function.

Q: Point out the error, if any in the program. #include <stdio.h> int main() { int i = 1; switch(i) { case 1: printf("Case1"); break; case 1*2+4: printf("Case2"); break; } return 0; }

Correct answer: No Errorcase 1*2+4 is a constant expression, which the compiler evaluates to 6 - that is allowed, and 6 does not clash with case 1. A default label is optional. So the program compiles and, with i equal to 1, prints Case1.

Q: What will be the output of the program? #include <stdio.h> int main() { int i=4; switch(i) { default: printf("This is default\n"); case 1: printf("This is case 1\n"); break; case 2: printf("This is case 2\n"); break; case 3: printf("This is case 3\n"); } return 0; }

Correct answer: This is default This is case 1i is 4, which matches no case, so control jumps to default - and default need not be last. Having no break, execution then falls through into case 1, whose break finally ends the switch. So two lines are printed.

21.

Output?

#include <stdio.h>
int main()
{
    int c = 5, no = 10;
    do {
        no /= c;
    } while(c--);
  
    printf ("%d\n", no);
    return 0;
}

A.1
B.Runtime Error
C.Compiler Error

Answer: B

Correct answer: Runtime Error

The loop divides no by c and then tests c--, so c falls 5, 4, 3, 2, 1, 0. On the pass after the test that saw c equal to 1, c is 0 - and no /= 0 is integer division by zero, which the hardware traps. The compiler cannot see it, so it is a run-time fault.

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22.

What is the output of the below program?

#include <stdio.h>
int main()
{
    int i = 0;
    switch (i)
    {
        case '0': printf("Geeks");
                break;
        case '1': printf("Quiz");
                break;
        default: printf("GeeksQuiz");
    }
    return 0;
}

A.Geeks
B.Quiz
C.GeeksQuiz
D.Compile-time error

Answer: C

Correct answer: GeeksQuiz

'0' is a character constant, and its value is the ASCII code 48, not the number 0. Likewise '1' is 49. The controlling expression is 0, which matches neither, so control falls to default.

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23.

When 2 is entered, The output of the code below is?

#include <stdio.h>
    void main()
    {
        int ch;
        printf("enter a value btw 1 to 2:");
        scanf("%d", &ch);
        switch (ch)
        {
        case 1:
            printf("1\n");
            break;
            printf("Hi");
        default:
            printf("2\n");
        }
    }

A.1
B.Hi 2
C.Run time error
D.2

Answer: D

Correct answer: 2

ch is 2, which matches no case, so control goes straight to default and prints 2. The printf("Hi") is unreachable in any event: it sits immediately after a break and before the next label, so no path can reach it.

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24.

Which of the following cannot be used as LHS of the expression in for (exp1;exp2; exp3) ?

A.Variable
B.Function
C.typedef
D.macros

Answer: D

Correct answer: macros

The three parts of a for are ordinary expressions, so anything assignable can appear on the left of an assignment in them - a variable, or the result of a function returning a modifiable lvalue. A macro is only text, replaced before compilation, so what appears in the code is whatever it expands to; it is not itself an object and cannot be assigned to.

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25.

Which of the following statement is correct for switch controlling expression?

A.Only int can be used in “switch” control expression
B.Both int and char can be used in “switch” control expression.
C.All types i.e. int, char and float can be used in “switch” control expression
D.“switch” control expression can be empty as well

Answer: B

Correct answer: Both int and char can be used in “switch” control expression.

The controlling expression must have an integer type. char qualifies - it is a small integer type and is promoted to int - as do short, long and enumerations. float and double do not, because equality against a case label would be unreliable for values that cannot be represented exactly. The expression also cannot be omitted.

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26.

The following code ‘for(;;)’ represents an infinite loop. Which statement exits the loop itself?

A.break
B.exit(0)
C.abort()
D.All of the mentioned

Answer: A

Correct answer: break

break is the statement that ends the loop: control passes to the statement after it and the program carries on. exit(0) and abort() would also stop the loop running, but only by ending the whole program, which is a different thing from leaving the loop.

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27.

Which keyword is used to come out of a loop only for that iteration?

A.break
B.continue
C.return
D.None of the mentioned

Answer: B

Correct answer: continue

continue abandons the current iteration and jumps to the next one - to the update expression in a for, or to the condition test in a while. break leaves the loop altogether, and return leaves the function.

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28.

Point out the error, if any in the program.

#include <stdio.h>
int main()
{
    int i = 1;
    switch(i)
    {
        case 1:
           printf("Case1");
           break;
        case 1*2+4:
           printf("Case2");
           break;
    }
return 0;
}

A.Error: in case 1*2+4 statement
B.Error: No default specified
C.Error: in switch statement
D.No Error

Answer: D

Correct answer: No Error

case 1*2+4 is a constant expression, which the compiler evaluates to 6 - that is allowed, and 6 does not clash with case 1. A default label is optional. So the program compiles and, with i equal to 1, prints Case1.

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29.

#include <stdio.h>   
int main() 
{ 
  int i;   
  for (i = 1; i != 10; i += 2) 
    printf(" GeeksQuiz "); 
  return 0; 
}

A.GeeksQuiz GeeksQuiz GeeksQuiz GeeksQuiz GeeksQuiz
B.GeeksQuiz GeeksQuiz GeeksQuiz .... infinite times
C.GeeksQuiz GeeksQuiz GeeksQuiz GeeksQuiz
D.GeeksQuiz GeeksQuiz GeeksQuiz GeeksQuiz GeeksQuiz GeeksQuiz

Answer: B

Correct answer: GeeksQuiz GeeksQuiz GeeksQuiz .... infinite times

i starts at 1 and rises by 2, so it takes only the odd values 1, 3, 5, 7, 9, 11, … and never equals 10. The test i != 10 is therefore never false. This is why < is safer than != in a loop condition whose variable moves by more than one.

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30.

What will be the output of the program?

#include <stdio.h>
int main()
{
    int i=4;
    switch(i)
    {
        default:
           printf("This is default\n");
        case 1:
           printf("This is case 1\n");
           break;
        case 2:
           printf("This is case 2\n");
           break;
        case 3:
           printf("This is case 3\n");
    }
    return 0;
}

A.This is defaultThis is case 1
B.This is case 3This is default
C.This is case 1This is case 3
D.This is default

Answer: A

Correct answer: This is default This is case 1

i is 4, which matches no case, so control jumps to default - and default need not be last. Having no break, execution then falls through into case 1, whose break finally ends the switch. So two lines are printed.

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