Conditional Statement in C Language

A program consists of many statements, which are to be executed based on some conditions. For example, a user wants to check whether a number is even or odd. Similarly, a user may check whether a year is a leap year or not? and many more. 

To perform these tasks, we need to write a program and execute the statements based on some conditions. C includes two conditional statements, if-else, and switch.

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Conditional Statement - if - else

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To check, whether a number is even or odd, if the number is divided by 2 and the remainder is 0 (zero), the number is even. If the remainder is not 0, the number is odd. Programmatically we can verify this number using the following code.

#include <stdio.h> int main (void) { int num; printf("This a program to check even or odd number!\n"); printf("Enter an integer: "); scanf("%d", &num); if(num % 2 == 0) { printf("The number is even."); } else { printf("The number is odd."); } return 0; }

In the above example, if the condition is true, the statement printf("The number is even."); is executed otherwise the statement printf("The number is odd."); is executed. Based on the problem statement, sometimes if-else may be used within if or else or both. Writing if-else within another if-else is known as nesting. In the following example, we are going to check leap-year.

#include <stdio.h> int main (void) { int year; printf("This a program to check leap year!\n"); printf("Enter a year: "); scanf("%d", &year); if(year % 4 == 0) { if(year % 100 == 0) { if(year % 400 == 0) { printf("Leap Year!\n"); } else { printf("Not Leap Year!\n"); } } else { printf("Leap Year!\n"); } } else { printf("Not Leap Year!\n"); } return 0; }

Another approach is to check leap year, where multiple conditions are checked together.

#include <stdio.h> int main() { int year; printf("\n Enter a year :"); scanf("%d", &year); if ((year % 4 == 0 && year % 100 != 0) || (year % 400 == 0)) printf("\n The year is a leap year."); else printf("\n The year is not a leap year."); return (0); }

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Conditional Statement - switch - case 

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C programming language has a built-in branch selection statement, which executes against a list of integer or character constants. These branches are known as cases. When a match is found to a case, the statements associated with that case are executed. Let us consider the following example of a basic calculator.

#include <stdio.h> int main(void) { int x, y, z, choice; printf("Calculator Program!\n"); printf("Enter value of x and y: "); scanf("%d %d", &x, &y); printf("Menu: 1 = add, 2 = sub, 3 = mul, 4 = div\n"); printf("Enter your choice: "); scanf("%d", &choice); switch(choice) { case 1: z = x + y; break; case 2: z = x - y; break; case 3: z = x * y; break; case 4: z = x / y; break; default: printf("You have entered wrong choice!"); } printf("The result is %d \n\n", z); return 0; }

In this program, first, we are taking two integer inputs for the variables x and y. Then we are taking the choice of the operation, which the user wants to perform. If the user enters 1 for the choice variable, case 1 will be executed. Similarly, other cases will be executed based on the value of choice. Please look at the switch-case block very carefully. At the end of every case (except the last case), we are using a break statement. If we don't use a break statement, all the statements followed by the case will also be executed until there is a break statement. This is not expected at all. After executing statements of the matching case, the control should go to the end of the switch case. Hence we should use a break statement at the end of every case. If none of these cases are matched, the statements of default are executed.

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Ternary Operator 

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Ternary operator checks if a condition is true or false and executes the expressions accordingly. Note that a ternary operator can be applied if the number of statements in a block is only one. If a block contains more than one statement, you have to use if - else blocks. Let us try to compare the ternary operator and if-else block.

#include <stdio.h> int main() { int score; printf("Enter your score:"); scanf("%d", &score); if (score >= 40) { printf("You are qualified!"); } else { printf("You are not qualified!"); } return 0; }

#include <stdio.h> int main() { int score; printf("Enter your score:"); scanf("%d", &score); (score >= 40) ? printf("You are qualified!") : printf("You are not qualified!"); return 0; }

Let us try another example, where a value is being assigned to a variable.

#include <stdio.h> int main() { int x, y, z; printf("Enter an integer value for x:"); scanf("%d", &x); printf("Enter an integer value for y:"); scanf("%d", &y); if (x >= y) { z = x; } else { z = y; } printf("Larger value is %d", z); return 0; }

#include <stdio.h> int main() { int x, y, z; printf("Enter an integer value for x:"); scanf("%d", &x); printf("Enter an integer value for y:"); scanf("%d", &y); z = (x >= y) ? x : y; printf("Larger value is %d", z); return 0; }

Happy Exploring!