By | 26.03.2017

# C Program to convert string of numbers to an integer

Write a C Program to convert string to number using Recursion. Here’s simple Program to convert string to number using Recursion in C Programming Language.

## 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;
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```

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