Control Flow & Decision Making

By default, code executes sequentially from top to bottom. Control flow statements allow the program to take branches and make decisions based on conditions.

1. The If-Else Statement

The if statement evaluates a condition. In C, any non-zero value is treated as true, and zero is treated as false:

#include <stdio.h>

int main() {
    int temperature = 28;

    if (temperature > 30) {
        printf("It's hot outside.\n");
    } else if (temperature >= 15) {
        printf("The weather is pleasant.\n");
    } else {
        printf("It's cold outside.\n");
    }
    return 0;
}

[!WARNING] In C, if you omit curly braces {} for an if or else block, only the single immediate statement following it is considered part of the conditional. It is a highly recommended convention to always use curly braces to avoid structural errors.

2. The Switch-Case Statement

The switch statement selects one of many code blocks to execute based on the value of a single variable. The variable must be an integer type (int or char):

#include <stdio.h>

int main() {
    char operator = '+';
    int a = 10, b = 5;

    switch (operator) {
        case '+':
            printf("Sum: %d\n", a + b);
            break; // Exits switch block
        case '-':
            printf("Difference: %d\n", a - b);
            break;
        default:
            printf("Unknown operator\n");
    }
    return 0;
}

Guide: If you omit the break; statement at the end of a case, execution will "fall through" into the next case, executing its statements as well. This is sometimes intentional but usually a bug.

3. The Ternary Operator

The ternary operator (? :) is a shorthand conditional expression:

// condition ? expression_if_true : expression_if_false
int age = 19;
char* status = (age >= 18) ? "Adult" : "Minor";