The following C program, using recursion, finds the first capital letter that exists in a string. We have included ctype.h in order to make use of “int isupper(char);” function that’s defined inside the ctype.h headerfile. The isupper finction returns 1 if the passed character is an uppercase and returns 0 is the passed character is a lowercase.
Here is the source code of the C program to find the first capital letter in a string using recursion. The C program is successfully compiled and run on a Linux system. The program output is also shown below.

/*
* C Program to find the first capital letter in a string using
* Recursion
*/
#include <stdio.h>
#include <string.h>
#include <ctype.h>

char caps_check(char *);

int main()
{
char string[20], letter;

printf("Enter a string to find it's first capital letter: ");
scanf("%s", string);
letter = caps_check(string);
if (letter == 0)
{
printf("No capital letter is present in %s.\n", string);
}
else
{
printf("The first capital letter in %s is %c.\n", string, letter); }
return 0;
}
char caps_check(char *string)
{
static int i = 0;
if (i < strlen(string))
{
if (isupper(string[i]))
{
return string[i];
}
else
{
i = i + 1;
return caps_check(string);
}
}
else return 0;
}



$ cc pgm32.c
$ a.out
Enter a string to find it's first capital letter: iloveC
The first capital letter in iloveC is C.