• Control Flow
• Branching
  • If
  • If-Else
  • If-Else if
  • Switch-Case
  • Conditional Operator ( ? : )
• Exercises

Control Flow is how we manage the path of statements, instructions, and function calls of a program. Without control flow, our program only moves from top to bottom (sequential). There are 2 types of control flow in C language: branching (selection) and repetition.

Branching allows us to specify which part of code to execute based on a condition. There are 4 ways we can implement branching in the C language, which are by using if, if-else, if-else if, and switch-case statements.

The syntax used in branching using if is as follows.

if (<Expressions / Conditions >) {

// Code to be executed if the condition is true

}

The way the if branch works is it checks and evaluates a condition to determine whether the next instruction in the bracket will be executed or not by the program.

• If the condition is TRUE (1), the code inside bracket will be executed.
• Otherwise if the condition is FALSE (0), the code inside bracket will not be executed.

Example:

For example, on a car dashboard there is a fuel indicator that will light up if the remaining fuel is less than a certain level (for example less than 10 litres). To evaluate the level of fuel, we ask: "Is the fuel less than 10 litres?".

In this case there is a condition

• If the fuel is less than 10 liters, then turn on the indicator light.

#include <stdio.h>
int main()
{
    int gasoline = 0;
    gasoline = 3;
    
    if (gasoline < 10) // If fuel is less than 10 liters
    {
         // Put here what needs to be done when the conditions are met
         printf ("The indicator light is on! \n");
    }
}

Output

The indicator light is on!

The syntax used in branching using if-else is as follows.

if (<Expression / Condition>) {

    // Code to be executed if the condition is true

} else {

    // Code to be executed if the condition is false

}

The way the if-else statement works is to check the conditions in the if.

• If the condition is TRUE (1), the program will execute the code inside the if bracket.
• Conversely, if the condition is FALSE (0), the code below else will be executed.

Example

For example, we want to find out whether someone is absent from class or not. If one is absent, their attendance will be crossed out (worth X), while **if present, then their attendance will be ticked (worth V) **.

So from this case, two alternative conditions are obtained.

• If he is present, then V appears
• If he is not present, X will appear

#include <stdio.h>
#define COME 1

int main ()
{
    int present = COME;
    if (present) // If the person is present
    {
        printf("V\n");
    } else {
        printf("X\n");
    }
}

Output

V

The syntax used in branching using if-else if statement is as follows.

if (<Expression / Condition>) {

    // Code to be executed if the condition is true

} else if (<Expression / Condition>) {

    // Code to be executed if the condition is false

}
// May add else {} if necessary

The way the if-else if branch works is to check the conditions in the if.

• If the condition evaluates to TRUE (1), the program will execute the code inside the if bracket.
• If the first condition not fulfilled, then it will check the condition in else if, if it evaluates to TRUE (1), then it will execute the command in that bracket, otherwise it will run the next sequence.
• If we provide an else statement at the end, then when all conditions in if and else ifs are not fulfilled or evaluate to FALSE (0), the program will automatically execute the command inside the else statement.

Apart from using the if statement to choose between many alternatives, there is also a switch statement which has the same function, which is to choose between many alternatives based on a condition. The condition in a switch statement contains an expression of a single variable of type int or char whose values will be checked in each case block.

Syntax for Switch-Case:

switch (expression) {
    case constant-expression :
        statement;
        break;

    case constant-expression :
        statement;
        break;
  
    /* You can have as many cases as possible */

    /* Default is compulsory to be added to the end of a switch-case statement.
       The below block of code will be executed when none of the cases above are fulfilled. */

    default:
        statement;
}

For each case block, the statement break must be added to the end, because if not then it will continue to run the case block underneath it until it meets another break or reaches the end of the switch block.

Example

#include <stdio.h>

int main()
{
    char plateNumber;
    printf("Enter the first letters of your license plate: ");
    scanf("%c", &plateNumber);
    
    switch (plateNumber)
    {
        case 'L':
            printf("Surabaya");
            break;

        case 'B':
            printf("Jakarta");
            break;

        case 'D':
            printf("Bandung");
            break;

        case 'N':
            printf("Malang / Lumajang");
            break;

        default:
            printf("Unknown plate number character");
    }
    return 0;
}

On the example above, the expression used is plateNumber, where the cases are the license plate letters: L, B, D, N, and so on.

The syntax for conditional operator is as follows:

(expression/condition) ? (expression if TRUE) : (expression if FALSE);

The conditional operator is the only ternary operator in C. The conditional operator acts like the if-else statement. The expression or condition to be evaluated is written before the question mark (?). If it evaluated to TRUE, then the program will execute the expression to the left of the colon (:). In opposite, if it evaluates to FALSE, then the program will execute the expression to the right of the colon.

Example:

#include <stdio.h>

int main()
{
    int mark;
    
    scanf("%d", &mark);
    printf(mark >= 75 ? "Lulus\n" : "Tidak Lulus\n");
    return 0;
}

The above program is equivalent to:

#include <stdio.h>

int main()
{
    int mark;
    
    scanf("%d", &mark);
    if (mark >= 75) {
        printf("Lulus\n");
    } else {
        printf("Tidak Lulus\n");
    }
    return 0;
}

Write a program that determines whether or not an input (0 to 999) is an Armstrong number.

Armstrong number is a number that is equal to the sum of cubes of its digits.

Sample Input 1

153

Sample Output 1

Is an Armstrong number

Sample Input 2

25

Sample Output 2

Is not an Armstrong number

Note: 153 is an Armstrong number because 153 = 1^3 + 5^3 + 3^3

Make a program that takes a number input between 0 to 999 and returns its value in letters (uses Bahasa Indonesia).

Sample Input 1

1

Sample Output 1

Satu

Sample Input 2

11

Sample Output 2

Sebelas

Sample Input 3

979

Sample Output 3

Sembilan ratus tujuh puluh sembilan

A, B, C, D, E, F, G are input signals of a digit from 0 to 9, as represented below.

Make a program that takes inputs I1, I2, I3, I4 and outputs the display of the seven input signals in binary (1 means the signal is turned on, 0 means the signal is turned off). (Inputs I1, I2, I3, and I4 are of binary notations. Example: 1 0 0 0 is equal to 8).

Sample Input 1

0 0 0 0

Sample Output 1

1 1 1 1 1 1 0

Sample Input 2

1 0 1 1

Sample Output 2

0 0 0 0 0 0 0