C String index

C Program to find character at index in a string

This program is used to find the character at index in a string and string is defined using pointers.

#include<stdio.h>                                                                
                                                                    
void main()                                                                     
{                                                                               
 char *str = "testing codingpointer.com";                                       
 int index;                                                                     
 char ch;                                                                       
 printf("Enter index: ");                                                       
 scanf("%d", &index);                                                           
 ch = str[index];                                                               
 printf("\ncharacter at index %d: %c\n", index, ch);                            
}                                                                             
                                                                                  

Output:

$ cc string-index.c
$ ./a.out 
Enter index: 5

character at index 5: n

we could also specify the index and string pointer variable reverse order like below which will also produce the same output.

#include<stdio.h>  

void main()                                                                     
{                                                                               
 char *str = "testing codingpointer.com";                                       
 int index;                                                                     
 char ch;                                                                       
 printf("Enter index: ");                                                       
 scanf("%d", &index);                                                           
 ch = index[str];                                                               
 printf("\ncharacter at index %d: %c\n", index, ch);                            
}

Output:

$ cc string-index.c
$ ./a.out 
Enter index: 8

character at index 8: c

This program is used to find the character at index in a string and string is defined using array.

#include<stdio.h>                                                             
                                                                                
void main()                                                                     
{                                                                               
 char str[] = "testing codingpointer.com";                                      
 int index;                                                                     
 char ch;                                                                       
 printf("Enter index: ");                                                       
 scanf("%d", &index);                                                           
 ch = str[index];                                                               
 printf("\ncharacter at index %d: %c\n", index, ch);                            
}                                                                               

Output:

$ cc string-index.c
$ ./a.out 
Enter index: 6

character at index 5: g

we could also specify the index and string array variable reverse order like below which will also produce the same output.

#include<stdio.h>                                                              
                                                                                
void main()                                                                     
{                                                                               
 char str[] = "testing codingpointer.com";                                      
 int index;                                                                     
 char ch;                                                                       
 printf("Enter index: ");                                                       
 scanf("%d", &index);                                                           
 ch = index[str];                                                               
 printf("\ncharacter at index %d: %c\n", index, ch);  

Output:

$ cc string-index.c
$ ./a.out 
Enter index: 9

character at index 8: o

C program to get starting character index in a string in one line

This c program is used to find the character starting index using one line in a string.

#include<stdio.h>                                                            
                                                                                
void main()                                                                     
{                                                                               
 char *str = "testing codingpointer.com";                                       
 int index;                                                                     
 char ch;                                                                       
 printf("Enter character: ");                                                   
 scanf("%c", &ch);                                                              
 for(index=0; *str++!=ch; index++);                                             
 printf("\ncharacter '%c' starting index: %d\n", ch, index);                    
}  

Output:

$ cc string-index.c
$ ./a.out 
Enter character: n

character 'n' starting index: 5

C program to find character starting index using while

#include<stdio.h>                                                        
                                                                                
void main()                                                                     
{                                                                               
 char str[] = "testing codingpointer.com";                                       
 int index=0;                                                                   
 char ch;                                                                       
 printf("Enter character: ");                                                   
 scanf("%c", &ch);                                                              
 while(*str++!=ch)                                                              
 {                                                                              
  index++;                                                                      
 }                                                                              
 printf("\ncharacter '%c' starting index: %d\n", ch, index);                    
}      

Output:

$ cc string-index.c
$ ./a.out 
Enter character: t

character 'n' starting index: 0

C program to find character ending index using while

#include<stdio.h>                                                              
                                                                                
void main()                                                                     
{                                                                               
 char str[] = "testing codingpointer.com";                                      
 int index = sizeof(str)/sizeof(str[0]);                                        
 char ch;                                                                       
 printf("Enter character: ");                                                   
 scanf("%c", &ch);                                                              
 while(*(str+(index-1))!=ch)                                                    
 {                                                                              
  index--;                                                                      
 }                                                                              
 printf("\ncharacter '%c' ending index: %d\n", ch, index+1);                    
} 

Output:

$ cc string-index.c
$ ./a.out 
Enter character: r

character 'r' ending index: 20

C program to find character ending index using while one line

#include<stdio.h>  

void main()                                                                     
{                                                                               
 char str[] = "testing codingpointer.com";                                      
 int index = (sizeof(str)/sizeof(str[0]))-1;                                    
 char ch;                                                                       
 printf("Enter character: ");                                                   
 scanf("%c", &ch);                                                              
 while(*(str+(index--))!=ch);                                                   
 printf("\ncharacter '%c' ending index: %d\n", ch, index+1);                    
}   

Output:

$ cc string-index.c
$ ./a.out 
Enter character: r

character 'r' ending index: 20

C program to find character ending index using while and pointer

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

void main()                                                                     
{                                                                               
 char *str = "testing codingpointer.com";                                       
 int index = strlen(str);                                                       
 char ch;                                                                       
 printf("Enter character: ");                                                   
 scanf("%c", &ch);                                                              
 while(*(str+(index--))!=ch);                                                   
 printf("\ncharacter '%c' ending index: %d\n", ch, index+1);                    
}    

Output:

$ cc string-index.c
$ ./a.out 
Enter character: r

character 'r' ending index: 20