C Exercises: Find the first capital letter in a string

C Recursion : Exercise-20 with Solution

Write a program in C to find the first capital letter in a string using recursion.

Pictorial Presentation:

Sample Solution:

#include <stdio.h>
#include <string.h>
#include <ctype.h> 
 
char checkCapital(char *);
 
int main()
{
    char str1[20], singLet;
	
    printf("\n\n Recursion : Find the first capital letter in a string :\n");
	printf("------------------------------------------------------------\n"); 	
 
    printf(" Input a string to including one or more capital letters : ");
    scanf("%s", str1);
    singLet = checkCapital(str1);
    if (singLet == 0)
    {
        printf(" There is no capital letter in the string :  %s.\n", str1);
    }
    else
    {
        printf(" The first capital letter appears in the string %s is %c.\n\n", str1, singLet);    }
        return 0;
    }
    char checkCapital(char *str2)
    {
        static int i = 0;
        if (i < strlen(str2))
        {
            if (isupper(str2[i]))
            {
                return str2[i];
            }
            else
            {
                i = i + 1;
                return checkCapital(str2);
            }
        }
        else return 0;
    }
	

Sample Output:

Recursion : Find the first capital letter in a string :                                                      
------------------------------------------------------------                                                  
 Input a string to including one or more capital letters : testString                                         
 The first capital letter appears in the string testString is S.

Explanation:

char checkCapital(char *str2)
    {
        static int i = 0;
        if (i < strlen(str2))
        {
            if (isupper(str2[i]))
            {
                return str2[i];
            }
            else
            {
                i = i + 1;
                return checkCapital(str2);
            }
        }
        else return 0;

The function checkCapital() takes a pointer to a string ‘str2’ as input and returns the first capital letter in the string, if there is any.

• The function uses recursion to iterate through the characters in the string.
• It starts by initializing a static variable i to zero.
• Then, it checks if the current character at index i in the string is a capital letter using the isupper() function from the ctype.h library.
• If it is a capital letter, the function returns that letter.
• Otherwise, it increments i by one and calls itself recursively to check the next character in the string.

If the function reaches the end of the string without finding a capital letter, it returns zero.

Time complexity and space complexity:

The time complexity of this function is O(n), where n is the length of the input string, since it needs to iterate through all the characters in the string.

The space complexity is O(1), since it only uses a constant amount of additional memory regardless of the size of the input.

Flowchart:

C Programming Code Editor:

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