Decision-making in C, as the name suggests, is a way of performing different sets of actions depending on various circumstances.

Shown below is the general form of a regular decision-making structure found in most of the programming languages −

Here, a particular condition statement is tested by the program, which returns true/false accordingly and executes further instructions.

C has three major decision-making instructions-

• if statement
• if-else statement
• switch statement

note: C programming language assumes any non-zero and non-null values as true, and if it is either zero or null, then it is assumed as a false value.

The if statement :

C uses the if keyword to implement the decision control instruction.

Syntax:

if(condition)
{
  //Statement executed if condition is true
}

Key points:

• The keyword if tells the compiler that what follows is a decision control instruction
• The condition following the if is always enclosed within a pair of parentheses.
• If the condition is true, then the statement is executed.
• If the condition is not true, then the statement is not executed; instead, the program skips past it.
• Generally, a condition is expressed using relational operators. For instance:

Expression	is true if
x==y	x is equal to y
x !=y	x is not equal to y
x>y	x is greater than y
x<y	x is less than y
x>=y	x is greater than or equal to y
x<=y	x is less than or equal to y

Example:

#include <stdio.h>

int main() {
    int num;
    printf("Enter a number:");
    scanf("%d",&num);
    if(num<10)
    {
        printf("Number is less than 10");
    }
    
    return 0;
}

Input : 3
Output:Number is less than 10
Input :21
Output: 

hence, we can see that no Result is displayed when the input is greater than 10.

Note: also read about  Format specifiers in C & Escape Sequence in C.

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