Write a C Program to convert string of numbers to an integer using Recursion

Recursion : :

• Recursion is the process of repeating items in a self-similar way. In programming languages, if a program allows you to call a function inside the same function, then it is called a recursive call of the function.

• The C programming language supports recursion, i.e., a function to call itself. But while using recursion, programmers need to be careful to define an exit condition from the function, otherwise it will go into an infinite loop.

• Recursive functions are very useful to solve many mathematical problems, such as calculating the factorial of a number, generating Fibonacci series, etc.

Below is the source code for C Program to convert string to number using Recursion which is successfully compiled and run on Windows System to produce desired output as shown below :

SOURCE CODE : :

/*  C Program to convert string to number */

#include<stdio.h>
#include<ctype.h>
void f(char *s, int *num);
int main()
{
        char str[10];
        int num;
        printf("Enter any string of numbers :");
        gets(str);
        num=0;
        f(str, &num);
        printf("\nAfter Converting String [ " %s " ] to Number = %d \n",str,num);

        printf("\nEnter any string of numbers :");
        gets(str);
        num=0;
        f(str, &num);
        printf("\nAfter Converting String [ " %s " ] to Number = %d \n",str,num);

        return 0;

}

void f(char *s, int *pnum)
{
    if(*s=='\0' || !isdigit(*s))
        return;
        *pnum = (*pnum)*10 + *s-'0';
    return f(s+1, pnum);
}

OUTPUT  : :

*************** OUTPUT **************


Enter any string of numbers :3456

After Converting String [ " 3456 " ] to Number = 3456

Enter any string of numbers :38543

After Converting String [ " 38543 " ] to Number = 38543