access an argument in a string pointer char* - c

Question

I need to try and fix sentences from an input in c, so I tried separating tokens and making new strings and then I wanted to access the first char of each string and make it a capital letter.
Now I am having trouble understanding how to access only one char of each new string, like trying to access only 'e' in hello which is in str1[0] second char.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
void main()
{
char str1[601], * str2[601];
int i = 0, j = 0;
printf_s("*************** Welcome to the text cleaner ***************\n\n");
printf_s("Please enter text:\n");
gets_s(str1, sizeof(str1));
char* sentence=NULL,*next_sentence=NULL;
sentence = strtok_s(str1,".",&next_sentence);
while (sentence != NULL)
{
printf(" %s\n", sentence);
str2[i++] = sentence;
sentence = strtok_s(NULL, ".", &next_sentence);
}
str2[i++] = '\0';
printf_s("%s", str2[1]);
}
Code and content of variables in debugger

Answer 1

Here is my take on what you are trying to do. I'm showing the code and the results. I have simplified your effort since you are mixing printf and printf_s. You use the _s variant for buffer overflow control. That does not seem to be your concern while simply learning about arrays.
Here is the code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
void main() {
char str1[601]; // This is an array of chars.
// If storing a string, final elem is 0x0
char *str2[601]; // This is a pointer to an array of chars.
//
int i = 0;
int j = 0;
// I removed your _s variants of standard libraries. Let's keep
// things simple.
printf("*************** Welcome to the text cleaner ***************\n\n");
printf("Please enter text:\n");
// ditto for gets to fgets
//
// Excerpt rom the manpage
//
// char *fgets(char *s, int size, FILE *stream);
//
// fgets() reads in at most one less than size characters from
// stream and stores them into the buffer pointed to by s.
// Reading stops after an EOF or a newline. If a newline is read,
// it is stored into the buffer. A terminating null byte ('\0')
// is stored after the last character in the buffer.
//
// fgets() returns s on success, and NULL on error or when end of
// file occurs while no characters have been read.
//str1 = fgets(str1, sizeof(str1), stdin);
// I would do a null check here.
if (NULL == fgets(str1, sizeof(str1), stdin)) {
return; // graceful exit
}
// Notice on the bracket print of your text, the closing >
// is shown on the next line. This is because its capturing the
// newline/carriage return character.
printf("You entered %d chars and the text was:\n<%s>\n", strlen(str1), str1);
// These are for your strtok operation
// I would call them tokens or words, but
// whatever.
char *sentence=NULL;
char *next_sentence=NULL;
// wants to parse a string
// Excerpt from manpage
//
// char *strtok(char *str, const char *delim);
// Ahh, now I see why you name is sentence. You
// are looking for periods to separage sentences.
printf("Lets use strtok\n");
sentence = strtok(str1, ".");
while (sentence != NULL) {
printf("A sentence is:\n %s\n", sentence);
str2[i++] = sentence;
sentence = strtok(NULL, ".");
}
// So now, your individual sentences are stored
// in the array str2.
// str2[0] is the first sentence.
// str2[1] is the next sentence.
//
// To access the characters, specify a sentence and
// then specify the character.
//
// You can do the math, but do a man ascii, look at
// difference in lowercase a and uppercase A in terms
// of ascii. If its not captializ3ed already, simply
// add that offset or error out if not in set a-z.
//
// Here I will just make the first letter of the second
// sentence to be J.
str2[1][0] = 'J';
// Note, since you are going to have in the 'space'
// since you are delimitting on '.', It will have the
// effect of replacing 'space' with 'J'.
printf("Sentence two is: \n%s\n", str2[1]);
}
Here is the code in action.
*************** Welcome to the text cleaner ***************
Please enter text:
John was here. and here.
You entered 25 chars and the text was:
<John was here. and here.
>
Lets use strtok
A sentence is:
John was here
A sentence is:
and here
A sentence is:
Sentence two is:
Jand here
I hope that helps. TLDR use str2[x][y] to access a string x at character y.