C program to Reverse a String using STACK

Reversing string is an operation of Stack by using Stack we can reverse any string, here we implemented a program in C - this will reverse given string using Stack.

Reverse a String using STACK

The logic behind to implement this program:

Read a string.
Push all characters until NULL is not found - Characters will be stored in stack variable.
Pop all characters until NULL is not found - As we know stack is a LIFO technique, so last character will be pushed first and finally we will get reversed string in a variable in which we store inputted string.

Reverse String using Stack using C program

/*C program to Reverse String using STACK*/

#include <stdio.h>
#include <string.h>

#define MAX 100	/*maximum no. of characters*/

/*stack variables*/
int top=-1;
int item;
/***************/

/*string declaration*/
char stack_string[MAX];

/*function to push character (item)*/
void pushChar(char item);

/*function to pop character (item)*/
char popChar(void);

/*function to check stack is empty or not*/
int isEmpty(void);

/*function to check stack is full or not*/
int isFull(void);
 
int main()
{
    char str[MAX];
    
    int i;
    
    printf("Input a string: ");
    scanf("%[^\n]s",str); /*read string with spaces*/
    /*gets(str);-can be used to read string with spaces*/
    
    for(i=0;i<strlen(str);i++)
        pushChar(str[i]);
        
    for(i=0;i<strlen(str);i++)
        str[i]=popChar();

    printf("Reversed String is: %s\n",str);
    
    return 0;
}
 
/*function definition of pushChar*/
void pushChar(char item)
{
    /*check for full*/
    if(isFull())
    {
        printf("\nStack is FULL !!!\n");
        return;
    }
    
    /*increase top and push item in stack*/
    top=top+1;
    stack_string[top]=item;
}
 
/*function definition of popChar*/
 char popChar()
{
    /*check for empty*/
    if(isEmpty())
    {
        printf("\nStack is EMPTY!!!\n");
        return 0;
    }

    /*pop item and decrease top*/
    item = stack_string[top];
    top=top-1;
    return item;
}
 
/*function definition of isEmpty*/
int isEmpty()
{
    if(top==-1)
        return 1;
    else
        return 0;
}

/*function definition of isFull*/ 
int isFull()
{
    if(top==MAX-1)
        return 1;
    else
        return 0;
}

Output

Input a string: Hello World!
Reversed String is: !dlroW olleH