Error : segmentation fault , core dumped , in c programming

Question

the following c programming code gives a core dump segmentation fault , please tell me why i am getting this error and help me by giving a corrected version of this code .Thank you!

#include <stdio.h>
#include <string.h>
 
int main()
{
    char str[100], ch;
    int i, Flag;
    Flag = 0;
 
    printf("\n Please Enter any String :  ");
    fgets(str,sizeof(str),stdin);
    printf("%s",str);
    printf("\n Please Enter the Character that you want to replace with :  ");
    scanf("%c", &ch);
    
    for(i = 0; i <= strlen(str); i++)
    {
          str[i]=ch;    
      }
    str[i]='\0';
    
    printf("\n The characters have been found and replaced with %c and they occur %d times ", ch, i + 1);
    printf("The replaced string is %s ",str);
    
    return 0;
}

Answer 1

Try this.

#include <stdio.h>
#include <string.h>
 
int main()
{
    char str[100], ch;
    int i, Flag;
    Flag = 0;
 
    printf("\n Please Enter any String :  ");
    fgets(str,sizeof(str),stdin);
    printf("%s",str);
    printf("\n Please Enter the Character that you want to replace with :  ");
    scanf("%c", &ch);
    
    for(i = 0; i < strlen(str); i++) //change <= to < 
    {
          str[i]=ch;      
      }
    str[i]='\0';
    
    printf("\n The characters have been found and replaced with %c and they occur %d times ", ch, i + 1);
    //printf("The replaced string is %s ",str);
    
    return 0;
}