fgets and basic string manipulation, C (gcc)

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#include  <stdio.h>

#define SIZE 30

/* It is very important to make sure you do not press "Enter" after you feed your
 string in the input (yellow pane). If you do so, nothing bad happens. However,
 there will be an "end of line" character at the end of the string.
 This character is counted toward the length of string. This is not a bug, it's 
 a feature! :-)
 */
 
int strlen(char *str) {
    int i = 0;
    
    //search for end of string to find the length of string
    while (str[i] != 0) {
        i++;
    } 
    return (i);
 }

int main(void)
{
    // my array for the string
    char myString[SIZE];
        
    int i = 0;
    
    printf("Example program for some string manipulations.\n\n");
    
    // First read in an input string
    if (fgets(myString, SIZE, stdin)) {
    
        //search for end of string to find the length of string
        while (myString[i] != 0) {
           printf("character %c @ index %d\n", myString[i], i);
           i++;
        }
        printf("\nLength of %s is %d using 'while' loop.\n", myString, i);  
     
     
        //another method to search for end of string  
        for (i=0; ;i++) {
             if (myString[i] == 0) 
                 break;
        }
        printf("Length of %s is %d using 'for' loop.\n", myString, i);    
            
        printf("Length of %s is %d using a function call.\n", myString, strlen(myString));  
        
    } else {
        printf("Error reading in the string!\n");
    }
    
    return 0;
}

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Compilation time: 0.12 sec, absolute running time: 0.14 sec, cpu time: 0 sec, memory peak: 3 Mb, absolute service time: 0,35 sec