Control Structures


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Conditional Statements

if (0) {
  printf("I am never run\n");
} else if (0) {
  printf("I am also never run\n");
} else {
  printf("I print\n");
}


// branching with multiple choices: switch()
switch (a) {
case 0: // labels need to be integral *constant* expressions
  printf("Hey, 'a' equals 0!\n");
  break; // if you don't break, control flow falls over labels
case 1:
  printf("Huh, 'a' equals 1!\n");
  break;
default:
  // if `some_integral_expression` didn't match any of the labels
  fputs("error!\n", stderr);
  exit(-1);
  break;
}

Loops

// While loops
int ii = 0;
while (ii < 10) { //ANY value not zero is true.
  printf("%d, ", ii++); // ii++ increments ii AFTER using its current value.
} // => prints "0, 1, 2, 3, 4, 5, 6, 7, 8, 9, "

printf("\n");

int kk = 0;
do {
  printf("%d, ", kk);
} while (++kk < 10); // ++kk increments kk BEFORE using its current value.
// => prints "0, 1, 2, 3, 4, 5, 6, 7, 8, 9, "

printf("\n");

// For loops
int jj;
for (jj=0; jj < 10; jj++) {
  printf("%d, ", jj);
} // => prints "0, 1, 2, 3, 4, 5, 6, 7, 8, 9, "

printf("\n");

// *****NOTES*****:
// Loops and Functions MUST have a body. If no body is needed:
int i;
for (i = 0; i <= 5; i++) {
  ; // use semicolon to act as the body (null statement)
}

Challenge

Here's a classic basic programming challenge. Write a program that prints the numbers from 1 to 50, but for multiples of three print “Fizz” instead of the number and for the multiples of five print “Buzz”. For numbers which are multiples of both three and five print “FizzBuzz”.

In C, use printf("text\n"); to print "text" with a newline and printf("%d\n", num); to print the number num with a newline. Make sure you print "FizzBuzz" together.

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