Program:

/*C program to split string by space into words.*/

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

int main()
{
    char str[100];
    char splitStrings[10][10]; //can store 10 words of 10 characters
    int i, j, cnt;

    printf("Enter a string: ");
    gets(str);

    j = 0;
    cnt = 0;
    for (i = 0; i <= (strlen(str)); i++) {
        // if space or NULL found, assign NULL into splitStrings[cnt]
        if (str[i] == ' ' || str[i] == '\0') {
            splitStrings[cnt][j] = '\0';
            cnt++; //for next word
            j = 0; //for next word, init index to 0
        }
        else {
            splitStrings[cnt][j] = str[i];
            j++;
        }
    }
    printf("\nOriginal String is: %s", str);
    printf("\nStrings (words) after split by space:\n");
    for (i = 0; i < cnt; i++)
        printf("%s\n", splitStrings[i]);
    
    return 0;
}

Output

Enter a string: Hello Guys This is a test string.

Original String is: Hello Guys This is a test string.
Strings (words) after split by space:
Hello
Guys
This
is
a
test
string.