In programming, control structures are fundamental elements that govern the flow of execution within a program. These structures enable decisions to be made, repetitive tasks to be handled efficiently, and the smooth progression of a program from one operation to another. They primarily include:

• Conditional Statements: if, else if, else, switch
• Loops: for, while, do-while
• Jump Statements: break, continue, return, goto

Conditional Statements

Conditional statements allow a program to make decisions and execute code blocks based on conditions.

a. if Statement

The if statement is the most basic form of decision-making. It allows code to be executed only if a particular condition is true.

Syntax:

if (condition) {
    // Block of code to be executed if the condition is true
}

Example:

int a = 10, b = 20;
if (a < b) {
    printf("a is less than b\n");
}

In this example, the condition a < b evaluates to true, so the message “a is less than b” is printed.

b. else Statement

The else statement complements if. It defines a block of code to execute if the if condition is false.

Syntax:

if (condition) {
    // Block of code if the condition is true
} else {
    // Block of code if the condition is false
}

Example:

int a = 10, b = 20;
if (a > b) {
    printf("a is greater than b\n");
} else {
    printf("a is less than or equal to b\n");
}

Here, since a > b is false, the else block will execute, printing “a is less than or equal to b”.

c. else if Statement

The else if statement allows you to test multiple conditions sequentially. As soon as one condition is met, the corresponding block is executed, and no further conditions are checked.

Syntax:

if (condition1) {
    // Block of code if condition1 is true
} else if (condition2) {
    // Block of code if condition2 is true
} else {
    // Block of code if none of the conditions are true
}

Example:

int marks = 85;
if (marks >= 90) {
    printf("Grade: A\n");
} else if (marks >= 75) {
    printf("Grade: B\n");
} else if (marks >= 60) {
    printf("Grade: C\n");
} else {
    printf("Fail\n");
}

In this example, the program checks conditions sequentially, and since marks >= 75 is true, it prints “Grade: B”.

Ternary Operation

In C, a ternary operator (? :) offers a shorthand way to write simple if-else statements. It is useful for cases where the if-else structure only involves assigning values or returning results based on a condition. This operator can reduce the verbosity of your code and make it more concise.

Basic Syntax:

condition ? expression_if_true : expression_if_false;

• condition: The logical condition to evaluate.
• expression_if_true: Executed if the condition is true.
• expression_if_false: Executed if the condition is false.

Example:

Using if-else:

int a = 10, b = 20;
int max;

if (a > b) {
    max = a;
} else {
    max = b;
}

Using the Ternary Operator:

int a = 10, b = 20;
int max = (a > b) ? a : b;

In this case, the ternary operator checks whether a > b and assigns a to max if true, otherwise assigns b to max.

Important Considerations:

• Readability: Ternary operators should be used sparingly for simple, short expressions. Overusing them, especially for more complex conditions or multiple operations, can reduce readability.
• Nesting: While ternary operators can be nested, this is discouraged because it can lead to difficult-to-read and maintain code.

Example of Nesting (Not recommended for complex cases):

int a = 10, b = 20, c = 5;
int max = (a > b) ? a : (b > c) ? b : c;

Here, the code checks if a > b first, and if not, it checks whether b > c. While this is valid syntax, it can quickly become unreadable if expanded further.

d. switch Statement

The switch statement is an alternative to multiple simple if-else statements. It tests the value of a single variable and executes one block of code depending on the case that matches the value.

Syntax:

switch (expression) {
    case constant1:
        // Block of code if expression equals constant1
        break;
    case constant2:
        // Block of code if expression equals constant2
        break;
    default:
        // Block of code if no case matches
}

Example:

int day = 3;
switch (day) {
    case 1:
        printf("Monday\n");
        break;
    case 2:
        printf("Tuesday\n");
        break;
    case 3:
        printf("Wednesday\n");
        break;
    default:
        printf("Invalid day\n");
}

Here, the value of day matches 3, so “Wednesday” is printed.

2. Looping Structures

Loops allow code to be executed repeatedly based on a condition.

a. for Loop

the for loop is commonly used for iterations where the number of repetitions is known beforehand.

Syntax:

for (initialization; condition; increment/decrement) {
    // Block of code to be executed
}

Example:

for (int i = 0; i < 5; i++) {
    printf("i = %d\n", i);
}

This loop initializes i to 0, checks if i is less than 5, and increments i after each iteration. It prints the value of i until i becomes 5.

b. while Loop

The while loop is used when the number of iterations is not known in advance, and the loop should continue as long as a condition is true.

Syntax:

while (condition) {
    // Block of code to be executed
}

Example:

int i = 0;
while (i < 5) {
    printf("i = %d\n", i);
    i++;
}

This loop continues until i reaches 5, printing the value of i at each step.

c. do-while Loop

The do-while loop is similar to the while loop, but the condition is evaluated after the loop body has executed. This ensures that the loop runs at least once.

Syntax:

do {
    // Block of code to be executed
} while (condition);

Example:

int i = 0;
do {
    printf("i = %d\n", i);
    i++;
} while (i < 5);

Here, the loop will execute the block of code at least once before checking the condition.

3. Jump Statements

Jump statements alter the normal flow of control by jumping directly to a specific part of the program or exiting from a block of code.

a. break Statement

The break statement is used to exit a loop or switch statement prematurely.

Example:

for (int i = 0; i < 10; i++) {
    if (i == 5) {
        break;
    }
    printf("i = %d\n", i);
}

In this example, when i equals 5, the break statement exits the loop, and the program stops printing values.

b. continue Statement

the continue statement skips the current iteration of the loop and moves to the next iteration.

Example:

for (int i = 0; i < 10; i++) {
    if (i == 5) {
        continue;
    }
    printf("i = %d\n", i);
}

When i equals 5, the continue statement skips printing and moves to the next iteration.

c. return Statement

The return statement exits a function and optionally returns a value to the calling function.

Example:

int sum(int a, int b) {
    return a + b;
}

In this function, return exits the function and returns the sum of a and b.

d. goto Statement

The goto statement allows for an unconditional jump to a labeled statement.

[!CAUTION] goto It is rarely used due to the potential for making code difficult to read.

Syntax:

goto label;
...
label:
    // Block of code

Example:

int i = 0;
if (i == 0) {
    goto skip;
}
printf("This won't be printed\n");
skip:
printf("This is printed\n");

Here, the goto statement jumps to the skip label, skipping the first printf statement.

Summary

Basic control structures enable effective control over the flow of execution in a program.

• Conditional Statements: Provide decision-making capabilities (if, else if, else, switch).

• Looping Constructs: Allow repetitive execution (for, while, do-while).

• Jump Statements: Alter the normal flow of execution (break, continue, return, goto).