1. 

int k;                                              int k;
int sum = 0;                                        int sum = 0;

                                                    k = 0;
for (k = 0; k < 50; k++) {         converted        while (k < 50) {
    sum = sum + k;                ==========>           sum = sum + k;
}                                                       k++;
                                                    }
													
printf("sum: %i\n", sum);                           printf("sum: %i\n", sum);

NOTE:  Everything is the same except:
  1. the "k = 0" is moved to just before the loop.
  2. the "k++" is moved to the last line in the loop.
  3. the word "while" is used instead of "for".
  

2.

int value = 0;
int sum = 0;
while (value >= 0) {
    fscanf(f, "%i", &value);
    sum = sum + value;
}
printf("Sum: %i\n", sum);



3.

int foo(char);

--- or ---

int foo(char x);

(using whatever variable name you like instead of "x").


4.

printf("Answer: %lf\n", power(7, 3.2));

-- or --
double a, b, answer;
a = 7;
b = 3.2;
answer = power(a, b);
printf("Answer: %lf\n", answer);


5.

The correct answer is (b):

    FILE * f = fopen("data.txt", "r");

NOTE:  the function name is "fopen()", not "open()".

NOTE:  you must have the star (*) as part of the type of the variable.  This
       makes it a "pointer", which will be discussed later in the course.

NOTE:  both parameters are text strings; you cannot forget the quotations marks around
       either the filename or the read-only specifier.