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C Program to Reverse Order of Words in a String

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How to write a C Program to Reverse Order of Words in a String with an example. For example, the tutorial gateway will become gateway tutorial

C Program to Reverse Order of Words in a String Example 1

This program to reverse words in a string in c allows the user to enter a string (or character array), and a character value. Next, it will reverse the order of words inside a string.

/* C Program to Reverse Order of Words in a String */
 
#include <stdio.h>
#include <string.h>
 
int main()
{
  	char str[100];
  	int i, j, len, startIndex, endIndex;
 
  	printf("\n Please Enter any String :  ");
  	gets(str);
  	
  	len = strlen(str);
  	endIndex = len - 1;
  	
  	printf("\n *****  Given String in Reverse Order  ***** \n"); 	   	
  	for(i = len - 1; i >= 0; i--)
	{
		if(str[i] == ' ' || i == 0)
		{
			if(i == 0)
			{
				startIndex = 0;
			}
			else
			{
				startIndex = i + 1;
			}
			for(j = startIndex; j <= endIndex; j++)
			{
				printf("%c", str[j]);
			}
			endIndex = i - 1;
			printf(" ");				
		} 
	}
	
  	return 0;
}

OUTPUT

C Program to Reverse Order of Words in a String 1

ANALYSIS
Within this C Program to reverse words in a string Here, we used For Loop to iterate each and every character in a String, and remove all the duplicate characters in it..

for(i = len - 1; i >= 0; i--)
{
	if(str[i] == ' ' || i == 0)
	{
		if(i == 0)
		{
			startIndex = 0;
		}
		else
		{
			startIndex = i + 1;
		}
		for(j = startIndex; j <= endIndex; j++)
		{
			printf("%c", str[j]);
		}
		endIndex = i - 1;
		printf(" ");				
	} 
}

User entered values in this C program to reverse words in a string

str[] = Hello World
len = 11
endIndex = len – 1 = 10

For Loop – First Iteration: for(i = len – 1; i >= 0; i–)
for(i = 10; 10 >= 0; 10–)
Next, it will enter into the If Statement to check whether the str[i] is equal to empty space or i = 0
This condition will be true once it reaches to empty space after World
for(i = 5; 5 >= 0; 5–)
if(str[5] == ‘  ‘ || 5 == 0) – Condition is True so, it will enter into next If statement
if(i == 0) => if(5 == 0) – Condition is False so, statement inside the else block will be executed
startIndex = i + 1
startIndex = 6

Second For Loop – First Iteration: for(j = startIndex; j <= endIndex; j++)
=> for(j = 6; 6 <= 10; 6++)
Within the For Loop we used printf statement to print single character
printf(“%c”, str[j]) => W

Do the same for j = 7, j = 8, j= 9, and j = 10

Next, it will start the First For Loop iteration where i = 4.
Do the same for i = 4, i = 3, i = 2, i = 1 and i = 0 in the reverse words in a given string in c program

C Program to Reverse Order of Words in a String Example 2

This reverse words in a string in c program will traverse the string from the end position to start position. Once it finds empty space, it will replace the empty space with a NULL value, and prints the string after that Null value.

/* C Program to Reverse Order of Words in a String */
 
#include <stdio.h>
#include <string.h>
 
int main()
{
  	char str[100];
  	int i, len;
 
  	printf("\n Please Enter any String :  ");
  	gets(str);
  	
  	len = strlen(str);
  	printf("\n *****  Given String in Reverse Order  ***** \n"); 	   	
  	for(i = len - 1; i >= 0; i--)
	{
		if(str[i] == ' ')
		{
			str[i] = '\0';
			printf("%s ", &(str[i]) + 1);	
		} 
	}
	printf("%s", str);
	
  	return 0;
}

OUTPUT

C Program to Reverse Order of Words in a String 2

C Program to Reverse Order of Words in a String Example 3

This program to reverse words in a string in c is the same as the first example, but this time we are saving the reverse order words in a separate string.

/* C Program to Reverse Order of Words in a String */
 
#include <stdio.h>
#include <string.h>
 
int main()
{
  	char str[100], revstr[100];
  	int i, j, index, len, startIndex, endIndex;
 
  	printf("\n Please Enter any String :  ");
  	gets(str);
  	
  	len = strlen(str);
  	index = 0;
  	endIndex = len - 1;
  	
  	printf("\n *****  Given String in Reverse Order  ***** \n"); 	   	
  	for(i = len - 1; i > 0; i--)
	{
		if(str[i] == ' ')
		{
			startIndex = i + 1;

			for(j = startIndex; j <= endIndex; j++)
			{
				revstr[index] = str[j];
				index++;
			}
			revstr[index++] = ' ';
			endIndex = i - 1;				
		} 
	}
	for(i = 0; i <= endIndex; i++)
	{
		revstr[index] = str[i];
		index++;
	}
	revstr[index] = '\0';
	printf("\n Given String in Reverse Order = %s", revstr); 
  	return 0;
}

OUTPUT

C Program to Reverse Order of Words in a String 3