C program to replace a word in a text by another given word

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I need help with an exercise in C. This is what I tried to do, but it doesn't work.

C

int main()
{
    int i, leng;
    char phrase[DIM], word[DIM], word2[DIM];

    printf("Write a sentence\n>>");
    fgets(phrase, sizeof(phrase), stdin);

    printf("Enter the word you want to replace in the sentence\n>> ");
    fgets(word, sizeof(word), stdin);

    printf("What do you want to replace it with?\n>> ");
    fgets(word2, sizeof(word2), stdin);

    leng = strlen(phrase);

    for(i = 0; i < leng; i++){
        if(phrase[i] == word){
            phrase[i] = word2;
        }
    }
    printf("%s", phrase);

When I start it, these warnings appear:

assignment to ‘char’ from ‘char *’ makes integer from pointer without a cast [-Wint-conversion]

comparison between pointer and integer

What I have tried:

I tried to use strcmp, but i don't know how to use it with this exercise

Posted 6-Jan-21 12:01pm

Member 15039311

Updated 6-Jan-21 20:20pm

CPallini

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k5054 · Answer 1 · 2021-01-06T12:56:00

C

char phrase[DIM], word[DIM], word2[DIM];
/* ... */
  if(phrase[i] == word)
      phrase[i] = word2;

phrase, word and word2 are all single dimension arrays of characters. Thus the expression

C

phrase[i] == word

attempts to compare the single character at phrase[i] with the contents of the variable word e.g.

'c' == "hello"

Similarily

C

phrase[i] = word2

attempts to assign a string of characters to a single char.
In each case, the C compiler is trying to assign or compare the address of the word or word2 varialbe to the single char contained in phrase[i].

What you want is to use strcmp(), or perhaps strncmp() to compare strings. You'll then need to figure out how to paste the replacement string into the original one. You might be tempted to use strcpy(), and it can be done using that, but you need to be careful. Consider, if your original phrase is "all dogs go to heaven" and you want to replace "dogs" with "elephants", you want to make sure you don'e end up with "all elephantso heaven".

You may also want to look at the man page for strstr(), which might help you find the string to replace. But again, be careful, since, if your starting phrase is "six yelling yellers yell loudly", and you want to replace "yell" with "shout", strstr() doesn't care about word delimiters, so will find the first occurence of "yell", so you could end up with "six shouting yellers yell loudly", which might not be what is wanted.

You might also want to look at the man page for strtok(), which might help with analyzing the original phrase.

CPallini · Answer 2 · 2021-01-06T20:20:00

Solution 2

Make sure you understand how strings work in C and then use the sample code in this page strstr - C++ Reference[^] as starting point (note: your task is a bit more difficult).

Posted 6-Jan-21 20:20pm