C Tutorial/Statement/If statement

Checking for a Range of Values

<source lang="cpp">#include <stdio.h> main() {

 int iResponse = 0;
 printf("Enter a number from 1 to 10: ");
 scanf("%d", &iResponse);
 if ( iResponse < 1 || iResponse > 10 )
   printf("\nNumber not in range\n");
 else
   printf("\nThank you\n");

}</source>

Enter a number from 1 to 10: 2
      
      Thank you

if Comparisons and Their Opposites

if Comparison else Statement Executed By This Condition < >= == != > <= <= > >= < != ==

if statement

To conditionally execute statements, you can use the if or the if...else statement.

The general form of the if statement is

<source lang="cpp">if(expr) {

   s1 ;
   s2 ;
   ....
 }</source>

if statement: compare the value from user input

<source lang="cpp">#include <stdio.h> int main(void) {

 int number = 0;
 printf("\nEnter an integer between 1 and 10: ");
 scanf("%d",&number);
 if (number > 5)
   printf("You entered %d which is greater than 5\n", number);
 if (number < 6)
   printf("You entered %d which is less than 6\n", number);
 return 0;

}</source>

Enter an integer between 1 and 10: 5
     You entered 5 which is less than 6

if statement with two else statements

<source lang="cpp">#include <stdio.h>

1. include <stdlib.h>

int main() {

   char num[2];
   int number;

   printf("Enter a number from 0 to 9:");
   gets(num);
   number=atoi(num);

   if(number<5)
   {
       printf("That number is less than 5!\n");
   }
   else if(number==5)
   {
       printf("You typed in 5!\n");
   }
   else
   {
       printf("That number is more than 5!\n");
   }

   return(0);

}</source>

Enter a number from 0 to 9:2
      That number is less than 5!

If with else statement

The general format for an if-else statement is

<source lang="cpp">if (condition)

  simple or compound statement  

else

  simple or compound statement.</source>

Operators Used in if Comparisons

Comparison Meaning or Pronunciation "True" Example < Less than 1 < 5, 8 < 9 == Equal to 7 == 7, 1 == 1 > Greater than 7 > 5, 10 > 0 <= Less than or equal to 4 <= 5, 8 <= 8 >= Greater than or equal to 6 >= 5, 2 >= 2 != Not equal to 1 != 0, 1 != 3.99

The if-else-if statement

The general format for the if-else if statement is:

<source lang="cpp">if (condition 1)

  simple or compound statement  

else if (condition 2)

  simple or compound statement  

else if ( condition 3)

  simple or compound statement  
  .....

else if ( conditon n )

  simple or compound statement</source>

The if statement: a compound statement

If a compound statement is used, it must be enclosed in opening and closing braces.

<source lang="cpp">#include<stdio.h> main() {

  int i=5, j =1;
  
   if (i > j){
       i = i + 1;
       printf("%d",i);
   }   
   else
       j = j +1;

}</source>

6

To execute only one statement, opening and closing braces are not required

<source lang="cpp">#include <stdio.h> main(){

 int i = 5;
 if(i > 0)
    printf(" i > 0. \n");
    

}</source>

i > 0.

Use compound conditions to check for upper and lowercase letters

<source lang="cpp">#include <stdio.h> main(){

   char cResponse = "\0";
   printf("Enter the letter A: ");
   scanf("%c", &cResponse);
   if ( cResponse== "A" || cResponse == "a" )
      printf("\nCorrect response\n");
   else
      printf("\nIncorrect response\n");

}</source>

Enter the letter A: 1
      
      Incorrect response

Use isdigit Function in if statement

<source lang="cpp">#include <stdio.h>

1. include <ctype.h>

main() {

 char cResponse = "\0";
 printf("\nPlease enter a letter: ");
 scanf("%c", &cResponse);
 if ( isdigit(cResponse)== 0 )
   printf("\nThank you\n");
 else
   printf("\nYou did not enter a letter\n");

}</source>

Please enter a letter: 1
      
      You did not enter a letter

Using nested ifs

<source lang="cpp">#include <stdio.h>

1. include <limits.h>

int main(void) {

 long test = 0L;              

 if( test % 2L == 0L) {
   printf("The number %ld is even", test);
   if ( (test/2L) % 2L == 0L)
   {
     printf("\nHalf of %ld is also even", test);
     printf("\nThat"s interesting isn"t it?\n");
   }
 }
 else
   printf("The number %ld is odd\n", test);
 return 0;

}</source>

The number 0 is even
     Half of 0 is also even
     That"s interesting isn"t it?