Control Structures (If-else, Loops)
Expert Answer & Key Takeaways
Detailed explanation of decision-making statements (if, else-if, switch) and looping constructs (for, while, do-while) in C programming.
Control Structures in C
In C programming, the default execution flow is sequential (line by line). However, 'Control Structures' allow programmers to alter this flow, enabling decision-making and repetitive execution based on specific conditions.
1. Decision Making Statements (Conditional Statements)
These statements execute a block of code only if a specific condition is evaluated as true (non-zero).
1.1 The if Statement
The simplest control structure. It evaluates a condition; if the condition is true, the code inside the
{} is executed. If false, it is skipped.if (age >= 18) {
printf("You can vote.");
}1.2 The if-else Statement
Provides an alternative path. If the condition is true, the
if block executes. If it is false, the else block executes.if (number % 2 == 0) {
printf("Even number");
} else {
printf("Odd number");
}1.3 The else if Ladder
Used to test multiple conditions sequentially. As soon as one condition evaluates to true, its block is executed, and the rest of the ladder is skipped.
if (marks >= 90) {
printf("Grade A");
} else if (marks >= 80) {
printf("Grade B");
} else {
printf("Fail");
}1.4 The switch Statement
A cleaner alternative to a long
else-if ladder when testing a single variable against multiple constant values.- Must use
caseto define values. - The
breakkeyword stops the switch block. Without it, execution 'falls through' to the next cases. - The
defaultcase executes if no match is found.
switch (dayNumber) {
case 1:
printf("Monday");
break;
case 2:
printf("Tuesday");
break;
default:
printf("Invalid Day");
}2. Looping (Iteration) Statements
Loops allow a block of code to be executed repeatedly as long as a specified condition remains true.
2.1 The while Loop (Entry-Controlled Loop)
The condition is checked before entering the loop body. If the condition is false initially, the loop body may not execute even once.
int i = 1; // Initialization
while (i <= 5) { // Condition
printf("%d ", i);
i++; // Update
}
// Output: 1 2 3 4 52.2 The do-while Loop (Exit-Controlled Loop)
The condition is checked after the loop body executes. Therefore, a
do-while loop is guaranteed to execute at least once, regardless of the condition.int i = 10;
do {
printf("Hello"); // This prints once even though 10 is not < 5
i++;
} while (i < 5);2.3 The for Loop
The most commonly used loop when the exact number of iterations is known in advance. It condenses initialization, condition, and update into a single line.
// Syntax: for (initialization; condition; update)
for (int i = 1; i <= 5; i++) {
printf("%d ", i);
}3. Jump Statements
Jump statements transfer the control of the program to another part unconditionally.
3.1 break
Used to immediately exit the innermost loop or
switch statement. Control passes to the statement directly following the loop.3.2 continue
Used inside loops to skip the current iteration and immediately jump to the next iteration (it goes to the update/condition check step).
for (int i = 1; i <= 3; i++) {
if (i == 2) {
continue; // Skips printing '2'
}
printf("%d ", i);
}
// Output: 1 33.3 goto
Transfers control to a labeled statement in the program. Generally discouraged in modern programming as it creates confusing 'spaghetti code'.
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