C If Statements

C programming provides conditional statements, which allows you to execute certain statements based on a condition. The most commonly used conditional statements in C programming are if statements, if else statements, if else if statements, and nested if statements.

If Statements

The if statement is used to execute a statement or a block of statements if a condition is true. The syntax for the if statement is as follows:

1if (condition) {
2   // statements to be executed if condition is true
3}

Here, the condition is an expression that evaluates to a boolean value, either true or false. If the condition is true, the statements inside the if statement are executed. If the condition is false, the statements inside the if statement are skipped.

Example:

1#include <stdio.h>
2
3int main(void) {
4    int num;
5    printf("Enter a number: ");
6    scanf("%d", &num);
7
8    if (num > 0) {
9        printf("The number is positive.\n");
10    }
11    return 0;
12}

In this example, the user is prompted to enter a number. The value of the num variable is then checked against 0 using the if statement. If num is greater than 0, the message "The number is positive" is printed.

If else Statements

The if else statement is used to execute a statement or a block of statements if a condition is true and another statement or block of statements if the condition is false. The syntax for the if else statement is as follows:

1if (condition) {
2   // statements to be executed if condition is true
3} else {
4   // statements to be executed if condition is false
5}

Example:

1#include <stdio.h>
2
3int main(void) {
4    int num;
5    printf("Enter a number: ");
6    scanf("%d", &num);
7
8    if (num > 0) {
9        printf("The number is positive.\n");
10    } else {
11        printf("The number is negative.\n");
12    }
13    return 0;
14}

In this example, the user is prompted to enter a number. The value of the num variable is then checked against 0 using the if else statement. If num is greater than 0, the message "The number is positive" is printed. If num is not greater than 0, the message "The number is negative" is printed.

If else if Statements

The if else if statement in C programming allows you to execute multiple conditions based on different inputs. It is an extension of the basic if statement, but allows you to test for multiple conditions, rather than just one. The syntax for the if else if statement is as follows:

1if (condition 1) {
2   // statements to be executed if condition 1 is true
3} else if (condition 2) {
4   // statements to be executed if condition 1 is false and condition 2 is true
5} else if (condition 3) {
6   // statements to be executed if condition 1 and 2 are false and condition 3 is true
7} ...

In the above syntax, condition 1, condition 2, and condition 3 are expressions that evaluate to either true or false. If condition 1 is true, then the statements within the first block will be executed, and the program will skip all other conditions. If condition 1 is false, the program will move on to check condition 2, and so on. If none of the conditions are met, the program will move on to the next section of code.

Here's an example that demonstrates how the if else if statement can be used:

1#include <stdio.h>
2
3int main(void) {
4    int grade;
5    printf("Enter your grade: ");
6    scanf("%d", &grade);
7    if (grade >= 90) {
8        printf("You received an A.\n");
9    } else if (grade >= 80) {
10        printf("You received a B.\n");
11    } else if (grade >= 70) {
12        printf("You received a C.\n");
13    } else if (grade >= 60) {
14        printf("You received a D.\n");
15    } else {
16        printf("You received an F.\n");
17    }
18    return 0;
19}

In this example, the user is prompted to enter a grade. The value of the grade variable is then checked against various ranges using the if else if statement. If the grade is 90 or above, the message "You received an A" is printed. If the grade is between 80 and 89, the message "You received a B" is printed, and so on. If none of the conditions are met, the message "You received an F" is printed.

Nested If Statements

A if statement can be nested within another if statement. This means that an if statement can be used inside the body of another if statement. The syntax for a nested if statement is as follows:

1if (condition 1) {
2   // statements to be executed if condition 1 is true
3   if (condition 2) {
4      // statements to be executed if condition 2 is true
5   }
6}

Example:

1#include <stdio.h>
2
3int main(void) {
4    int num1, num2;
5    printf("Enter two numbers: ");
6    scanf("%d %d", &num1, &num2);
7
8    if (num1 > num2) {
9        printf("The first number is greater than the second number.\n");
10        if (num1 >= 100) {
11            printf("The first number is greater than or equal to 100.\n");
12        }
13    } else {
14        printf("The second number is greater than or equal to the first number.\n");
15    }
16    return 0;
17}

In this example, the user is prompted to enter two numbers. The value of the num1 and num2 variables are then checked against each other using the outer if statement. If num1 is greater than num2, the message "The first number is greater than the second number" is printed. Then, the inner if statement checks if num1 is greater than or equal to 100. If num1 is greater than or equal to 100, the message "The first number is greater than or equal to 100" is printed. If num1 is not greater than num2, the message "The second number is greater than or equal to the first number" is printed.