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Problem 1. Basic knowledge

1. Select the correct statement(s).

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• We can setup our own IDE (Integrated Development Environment) by having VSCode configured with some extensions, compilers and debuggers.
• C++23 is the latest C++ standard released in 2023. If we want to write code in C++23, we should upgrade VSCode to the latest version.
• GCC can only support Windows. In Linux, we must use Clang.
• A C program can be executed directly by the computer without being transformed into an executable file.
• We can compile and run C/C++ programs in the terminal.
• VSCode and CLion are different types of C/C++ compilers.

2. Fill in the blanks. For the column "Signedness", write either signed or unsigned. If the answer to any of the blanks is implementation-defined, write id.

3. Suppose int is 32-bit. Suppose we have the following variable declarations.

int ival = 45;
double dval = 3.14;
unsigned uval = -5;

Write down the type and the value of each of the expressions in the following table. If the type is floating-point, round the value to 2 decimal places. If a type has more than one names, write the shortest one, e.g. write int for signed int.

4. Suppose c is a variable of type char. If c is a decimal digit character, how can we obtain its numeric value?

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• c - '\0'
• c - '0'
• int(c)
• c - 0
• c - 48
• ord(c) - '0', where ord is a standard library function that is used to obtain the ASCII value of c.

5. Regarding undefined behaviors, which of the following statements is/are true?

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• An undefined behavior means that two or more behaviors are permitted by the standard and that the compiler will choose a meaningful one. The behavior remains unchanged when the program is run again, although we don't know what the behavior is.

• An undefined behavior means that program calls to undeclared or undefined functions.

• An undefined behavior means that there are no restrictions on the behavior of the program. The standard does not require such programs to do anything meaningful.

• An undefined behavior results in one of a set of valid results. For example, the following code (assuming int is 32-bit) will assign the variable x with some value, but we don't know what the value is.

  int ival = 10000000;
  int x = ival * ival;
  

• Correct C programs shall not have undefined behaviors.

6. Suppose int is 32-bit and long long is 64-bit. Select the code snippet(s) that involve(s) integer overflow.

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• unsigned u1 = 10000001;
  u1 = u1*u1*u1*u1*u1;
  

• int inf = 42 / 0;
  

• long long ival = -1000000000000000;
  unsigned uval = ival;
  

• int ival = 10000000;
  long long llval = ival * ival;
  

7. Suppose int is 32-bit. Select the code snippet(s) that involve(s) undefined behavior.

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• unsigned uval = -111;
  printf("%u%%\n", uval);
  

• int x = 96;
  printf("%f\n", x/100);
  

• int i = 42;
  printf("%d%d\n", ++i, i);
  

• int helper(int value) {
    printf("value is %d\n", value);
  }
  int main(void) {
    int x = helper(42);
    int y = helper(x);
    printf("%d\n", x + y);
  }
  

• int random(void) {
    int x;
    return x;
  }
  int main(void) {
    printf("%d\n", random());
  }
  

• double lim(int condition, double formula){
      double d = 0.000618, dx = 1.0;
      return condition ? 0 : d*formula/dx;
  }
  int main(void){
      int _x = 1, x = 4399, inf = 2147483647;
      double e = lim(_x --> inf, (1 + 1/x)^x);
  }