How to use if - else statement in C / C++
In this tutorial, we will learn about if - else
statement in C / C++ and its working with the help of some examples. This is one of the basic knowledge in C / C++ programming language, so please learn it carefully.
In C / C++ programming, if - else
statement is used to execute a block of code in a certain condition. There are two cases:
- If condition is true: Execute block of code.
- If the condition is false: Skip the code block and execute the statements below.
For example: assigning grades (A, B, C) based on marks obtained by a student.
- If the percentage is above 90, assign grade A.
- If the percentage is above 75 and below 90, assign grade B.
- If the percentage is above 65 and below 75, assign grade C.
There are three forms of if - else
statements in C / C++.
if
statement in C / C++.if - else
statement in C / C++.if - else else - if
statement in C / C++.
Now, we will learn about each form of if - else
statement in C / C++ one by one.
if statement in C / C++
The if
statement in C / C++ is used in case we only have a single condition. That means, if the condition is true then do something and if the condition is false then skip.
The syntax of if statement in C / C++:
if (condition) { // body of if statement }
Here,
- condition: This is the condition of the
if
statement.- If the condition evaluates to true: The block of code inside the
if
statement body is executed. - If the condition evaluates to false: The block of code inside the
if
statement body is skipped.
- If the condition evaluates to true: The block of code inside the
*Note: Condition is placed inside ( )
and code block is placed inside { }
.
For example: Check positive with if
statement in C / C++.
C++ programming:
/* Program to print positive number entered by the user If the user enters a negative number, it is skipped */ #include <iostream> using namespace std; int main() { int number; cout << "Enter an integer: "; cin >> number; // checks if the number is positive if (number > 0) { cout << "You entered a positive integer: " << number << endl; } cout << "This statement is always executed."; cout<<"\n-------------------------------\n"; cout<<"This program is posted at learnnc.com"; return 0; }
C programming:
#include <stdio.h> int main(void) { int number; printf("Enter an integer: "); scanf("%d", &number); // checks if the number is positive if (number > 0) { printf("You entered a positive integer: %d\n",number); } printf("This statement is always executed."); printf("\n-------------------------------\n"); printf("This program is posted at learnnc.com"); return 0; }
Output:
if - else statement in C / C++
The if - else
statement is used in case of multiple conditions. Each condition will execute a different block of code.
The syntax of if - else
statement in C / C++:
if (condition) { // block of code if condition is true } else { // block of code if condition is false }
Explain:
- If the condition evaluates true:
- The code inside the body of the
if
is executed. - The code inside the body of the
else
is skipped from execution.
- The code inside the body of the
- if the condistion evaluates false:
- The code inside the body of the
else
is executed. - The code inside the body of the
if
is skipped from execution.
- The code inside the body of the
For example: Check even or odd number with if - else
statement in C / C++.
C++ programming:
#include <iostream> using namespace std; int main() { int number; cout << "Enter an integer: "; cin >> number; if (number % 2 == 0) { cout << "You entered a even number: " << number << endl; } else{ cout << "You entered a odd number: " << number << endl; } cout<<"\n-------------------------------\n"; cout<<"This program is posted at learnnc.com"; return 0; }
C programming:
#include <stdio.h> int main(void) { int number; printf("Enter an integer: "); scanf("%d", &number); if (number % 2 == 0) { printf("You entered a even number: %d\n",number); } else{ printf("You entered a odd number: %d\n",number); } printf("\n-------------------------------\n"); printf("This program is posted at learnnc.com"); return 0; }
Output:
if - else else - if statement in C / C++
The if - else else if
statement is used in case there are more than two alternatives.
The syntax of if - else else - if
statement in C / C++:
if (condition1) { // code block 1 } else if (condition2){ // code block 2 } else { // code block 3 }
Explain:
- If the
condition
1 is true: Theblock code 1
is executed. - if the
condition 1
is false: Theblock code 1
is skipped and thecondition 2
is evaluated.- If the
condition 2
is true: Theblock code 2
is excuted. - If the
condition 2
is false: Theblock code 3
is executed.
- If the
For example: Program to check whether an integer is positive, negative or zero.
C++ programming:
#include <iostream> using namespace std; int main() { int number; cout << "Enter an integer: "; cin >> number; if (number > 0) { cout << "You entered a positive integer: " << number << endl; } else if (number < 0) { cout << "You entered a negative integer: " << number << endl; } else { cout << "You entered 0." << endl; } cout<<"\n-------------------------------\n"; cout<<"This program is posted at learnnc.com"; return 0; }
C programming:
#include <stdio.h> int main(void) { int number; printf("Enter an integer: "); scanf("%d", &number); if (number > 0) { printf("You entered a positive integer: %d\n",number); } else if (number < 0) { printf("You entered a negative integer: %d\n",number); } else { printf("You entered 0.\n"); } printf("\n-------------------------------\n"); printf("This program is posted at learnnc.com"); return 0; }
Output 1:
Output 2:
Output 3:
Nestef if statement in C / C++
The nested if
statement occurs where one if
statement is inside another if
statement.
Think of it as a multi-class if
statement. The outer class is an if
statement and its inner class adds one more if
statement.
The syntax of nested if
statement in C / C++:
// outer if statement if (condition1) { // statements // inner if statement if (condition2) { // statements } }
For example: Program to check whether an integer is positive, negative or zero using nested if
statement in C / C++.
C++ programming:
#include <iostream> using namespace std; int main() { int number; cout << "Enter an integer: "; cin >> number; if(number != 0){ if (number > 0) { cout << "You entered a positive integer: " << number << endl; } else if (number < 0) { cout << "You entered a negative integer: " << number << endl; } } else { cout << "The number is 0 and it is neither positive nor negative." << endl; } cout<<"\n-------------------------------\n"; cout<<"This program is posted at learnnc.com"; return 0; }
C programming:
#include <stdio.h> int main(void) { int number; printf("Enter an integer: "); scanf("%d", &number); if(number != 0){ if (number > 0) { printf("You entered a positive integer: %d\n",number); } else if (number < 0) { printf("You entered a negative integer: %d\n",number); } } else { printf("The number is 0 and it is neither positive nor negative.\n"); } printf("\n-------------------------------\n"); printf("This program is posted at learnnc.com"); return 0; }
Output:
Body of if...else with only one statement
If the body of if - else
has only one statement, you can omit { }
in the program. This makes your program look cleaner.
if (condition){ //statement } //or if (condition) //statement
Example 1:
int number = 5; if (number > 0) { cout << "The number is positive." << endl; } else { cout << "The number is negative." << endl; }
Or
int number = 5; if (number > 0) cout << "The number is positive." << endl; else cout << "The number is negative." << endl;
if - else statement in C / C++ with examples
Here, we have two examples with if - else
statement in C/C++. The program is written in C and C++ languages.
Example 1: Find the largest of the three numbers with if - else
statement in C / C+.
C++ programming:
#include <iostream> using namespace std; int main() { int a, b, c, max; cout << "Enter number a = "; cin >> a; cout << "Enter number b = "; cin >> b; cout << "Enter number c = "; cin >> c; max = a; if(max < b) { max = b; } if(max < c) { max=c; } cout << "The largest of the three numbers " << a << ", " << b << ", " << c << " is: " << max; cout<<"\n-------------------------------\n"; cout<<"This program is posted at learnnc.com"; return 0; }
C programming:
#include <iostream> using namespace std; int main() { int a, b, c, max; cout << "Enter number a = "; cin >> a; cout << "Enter number b = "; cin >> b; cout << "Enter number c = "; cin >> c; max = a; if(max < b) { max = b; } if(max < c) { max=c; } cout << "The largest of the three numbers " << a << ", " << b << ", " << c << " is: " << max; cout<<"\n-------------------------------\n"; cout<<"This program is posted at learnnc.com"; return 0; }
Output:
Example 2: Check even and odd numbers with if - else
statement in C / C++.
C++ programming:
#include <iostream> using namespace std; int main() { int number; cout << "Enter an integer: "; cin >> number; if(number != 0){ if (number %2 == 0) { cout << "You entered a even number: " << number << endl; } else{ cout << "You entered a odd number: " << number << endl; } } else { cout << "This is zero." << endl; } cout<<"\n-------------------------------\n"; cout<<"This program is posted at learnnc.com"; return 0; }
C programming:
#include <stdio.h> int main(void) { int number; printf("Enter an integer: "); scanf("%d", &number); if(number != 0){ if (number %2 == 0) { printf("You entered a even number: %d\n",number); } else{ printf("You entered a odd number: %d\n",number); } } else { printf("This is zero\n"); } printf("\n-------------------------------\n"); printf("This program is posted at learnnc.com"); return 0; }
Output: