Control Flow

## Learning Objectives - Master if, else if, else statements - Understand switch statements - Learn for, while, do-while loops - Use break and continue ## if Statement ### Basic if ```c int age = 18; if (age >= 18) { printf("Adult\n"); } ``` ### if-else ```c int age = 15; if (age >= 18) { printf("Adult\n"); } else { printf("Minor\n"); } ``` ### if-else if-else ```c int score = 85; char grade; if (score >= 90) { grade = 'A'; } else if (score >= 80) { grade = 'B'; } else if (score >= 70) { grade = 'C'; } else if (score >= 60) { grade = 'D'; } else { grade = 'F'; } printf("Grade: %c\n", grade); ``` ## Ternary Operator ```c int age = 20; int status = (age >= 18) ? 1 : 0; ``` ## switch Statement ### Basic switch ```c int day = 3; char *dayName; switch (day) { case 1: dayName = "Monday"; break; case 2: dayName = "Tuesday"; break; case 3: dayName = "Wednesday"; break; case 4: dayName = "Thursday"; break; case 5: dayName = "Friday"; break; case 6: dayName = "Saturday"; break; case 7: dayName = "Sunday"; break; default: dayName = "Invalid"; } printf("%s\n", dayName); ``` ### Fall-through ```c switch (month) { case 1: case 3: case 5: case 7: case 8: case 10: case 12: days = 31; break; case 4: case 6: case 9: case 11: days = 30; break; case 2: days = 28; break; } ``` ## for Loop ### Basic for ```c for (int i = 0; i < 5; i++) { printf("%d\n", i); // 0, 1, 2, 3, 4 } ``` ### Loop Components ```c // for (init; condition; increment) for (int i = 0; i < 5; i++) { // body } ``` Is equivalent to: ```c int i = 0; // init while (i < 5) { // condition // body i++; // increment } ``` ### Infinite Loop ```c for (;;) { // Runs forever } while (1) { // Also runs forever } ``` ### Comma Operator in for ```c for (int i = 0, j = 10; i < 5; i++, j--) { printf("%d - %d\n", i, j); } ``` ## while Loop ### Basic while ```c int i = 0; while (i < 5) { printf("%d\n", i); i++; } ``` ### while with Condition First ```c #include int main(void) { char input[100]; while (scanf("%99s", input) == 1) { if (strcmp(input, "quit") == 0) { break; } printf("You entered: %s\n", input); } return 0; } ``` ## do-while Loop ### Executes at Least Once ```c int i = 0; do { printf("%d\n", i); i++; } while (i < 5); ``` ### Menu Example ```c #include int main(void) { int choice; do { printf("1. New Game\n"); printf("2. Load Game\n"); printf("3. Quit\n"); printf("Choose: "); scanf("%d", &choice); } while (choice < 1 || choice > 3); return 0; } ``` ## break and continue ### break - Exit Loop ```c for (int i = 0; i < 10; i++) { if (i == 5) { break; // Exit when i is 5 } printf("%d\n", i); // 0, 1, 2, 3, 4 } ``` ### continue - Skip Iteration ```c for (int i = 0; i < 5; i++) { if (i == 2) { continue; // Skip when i is 2 } printf("%d\n", i); // 0, 1, 3, 4 } ``` ## Nested Loops ```c for (int i = 0; i < 3; i++) { for (int j = 0; j < 3; j++) { printf("(%d,%d) ", i, j); } printf("\n"); } ``` Output: ```text (0,0) (0,1) (0,2) (1,0) (1,1) (1,2) (2,0) (2,1) (2,2) ``` ### Break from Nested Loop ```c for (int i = 0; i < 5; i++) { for (int j = 0; j < 5; j++) { if (j == 2) { break; // Breaks inner loop only } printf("%d,%d\n", i, j); } } ``` ## goto Statement ### Basic goto ```c for (int i = 0; i < 10; i++) { for (int j = 0; j < 10; j++) { if (j == 2) { goto done; // Jumps to label } } } done: printf("Found it!\n"); ``` ### Avoid goto **Note:** goto makes code hard to follow. Use break/continue with flags instead. ## Common Patterns ### Sum 1 to N ```c int sum = 0; for (int i = 1; i <= 100; i++) { sum += i; } ``` ### Find in Array ```c int numbers[] = {3, 7, 2, 9, 4}; int target = 9; int found = 0; for (int i = 0; i < 5; i++) { if (numbers[i] == target) { found = 1; break; } } ``` ### Count Matches ```c int numbers[] = {1, 2, 3, 2, 4, 2, 5}; int target = 2; int count = 0; for (int i = 0; i < 7; i++) { if (numbers[i] == target) { count++; } } ``` ### FizzBuzz ```c for (int i = 1; i <= 20; i++) { if (i % 15 == 0) { printf("FizzBuzz\n"); } else if (i % 3 == 0) { printf("Fizz\n"); } else if (i % 5 == 0) { printf("Buzz\n"); } else { printf("%d\n", i); } } ``` ## Summary - if/else if/else for conditional logic - switch for multiple discrete values - for loop for known iterations - while loop for condition-based iteration - do-while for at-least-once iteration - break exits loop; continue skips iteration - Avoid goto (makes code hard to follow)