Which keyword is used to come out of a loop only for that iteration?
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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What is the output of this C code?
void main()
{
int i = 0, j = 0;
for (i = 0;i < 5; i++)
{
for (j = 0;j < 4; j++)
{
if (i > 1)
break;
}
printf("Hi \n");
}
}
Answer: A
Correct answer: Hi is printed 5 times
The printf is outside the inner loop but inside the outer one, so it runs once per outer iteration - five times in all. The break only ever escapes the inner loop, and even then it changes nothing visible: whether the inner loop runs four times or stops at once, the outer loop still completes its five passes.
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What is the output of this C code?
void main()
{
int i = 0;
int j = 0;
for (i = 0;i < 5; i++)
{
for (j = 0;j < 4; j++)
{
if (i > 1)
continue;
printf("Hi \n");
}
}
}
Answer: B
Correct answer: Hi is printed 8 times
Here the printf is inside the inner loop, and continue skips it. For i equal to 0 and 1 the condition i > 1 is false, so all four inner passes print - \(2 \times 4 = 8\) lines. From i = 2 onwards continue fires on every inner pass and nothing more is printed.
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What is the output of this C code?
void main()
{
int i = 0;
if (i == 0)
{
printf("Hello");
continue;
}
}
Answer: D
Correct answer: Compile time error
continue is meaningful only inside a loop: it asks for the next iteration, and here there is no loop to iterate. Written inside a bare if with no enclosing loop, it is a compile-time error.
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What is the output of this C code?
int main()
{
printf("before continue ");
continue;
printf("after continue\n");
}
Answer: D
Correct answer: Compile time error
continue must appear inside a loop. In a function body with no loop around it there is no next iteration to jump to, so the compiler rejects the program - neither printf ever runs.
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The following code ‘for(;;)’ represents an infinite loop. Which statement exits the loop itself?
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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What is the correct syntax for running a for loop over two variables simultaneously?
Answer: B
Correct answer: for (i = 0, j = 0;i < n, j < n; i++, j += 5)
The comma operator lets a single for carry more than one initialisation and more than one update, so both variables advance together in one loop. Note the trap in the condition: i < n, j < n evaluates both but yields only the last, so it is really j < n that controls the loop - a genuine condition on both would need &&.
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Which of the following for loops covers the same range of values of i as for (i = 0; i < n; i++)?
Answer: D
Correct answer: for (i = n-1; i>-1; i--)
for (i = 0; i < n; i++) visits 0 to n-1. Running the same range backwards means starting at n-1 and continuing while i is still at least 0 - that is, while i > -1. The alternatives either start at n, which is out of range, or stop at i > 0, which misses the element at index 0.
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Which of the following cannot be used as LHS of the expression in for (exp1;exp2; exp3) ?
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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What is the output of this C code?
void main()
{
int k;
for (k = -3; k < -5; k++)
printf("Hello");
}
Answer: D
Correct answer: Nothing
A for tests its condition before the first pass. With k at -3, the test k < -5 is already false, so the body never runs and nothing is printed. (Had it been a do-while, the body would have run once.)
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