Replace spaces with %20, but doesn't print last word - c

Question

I'm currently doing the exercises from "Cracking the coding interview". And even though the answer to this problem seems to be in many versions out there. I'm not able to work mine properly.
I've checked the other versions in stackoverflow but I'm not able to find the difference or what's causing me this problem.
THE PROBLEM: it does change spaces for '%20' but it does not print the last word.
EXAMPLE:
Input: "Mr John Smith
Output: "Mr%20John%20"
I leave you here my code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
/* Maximum sentence size + 1. */
#define MAX_SENTENCE_SZ 256
int amountOfSpaces(char* str){
int cnt=0;
while(*str!='\0'){
if(*str == ' '){
cnt++;
}
str++;
}
return cnt;
}
int main(){
char sentence[100]={'\0'};
/* Get the sentence, with size limit. */
fgets (sentence, MAX_SENTENCE_SZ, stdin);
/* Remove trailing newline, if there. */
if ((strlen(sentence)>0) && (sentence[strlen (sentence) - 1] == '\n'))
sentence[strlen (sentence) - 1] = '\0';
int cant = amountOfSpaces(sentence);
int newleng = sizeof(sentence) + cant*2;
char *ans = (char *)malloc(newleng+sizeof(char));
int pos=0;
for(int i=0; i<= sizeof(sentence)-1; i++,pos++){
if (sentence[i] == ' ') {
ans[pos] = '%';
ans[pos + 1] = '2';
ans[pos + 2] = '0';
pos += 3;
} else {
ans[pos] = sentence[i];
}
}
ans[pos+1]='\0';
printf("%lu\n", sizeof(sentence));
printf("%lu\n", sizeof(ans));
printf("%s",ans);
/* Free memory and exit. */
free (ans);
return 0;
}

Answer 1

There are several errors in your code
don't call strlen every time you need the length, it computes the length, so it's expensive
sentenceLength = strlen(sentence);
/* Remove trailing newline, if there. */
if ((sentenceLength > 0) && (sentence[sentenceLength - 1] == '\0'))
sentence[--sentenceLength] = '\0';
int cant = amountOfSpaces(sentence);
You already have the length of the string, and sizeof sentence is 100, that is not the length of the string
int newleng = sentenceLength + 2 * cant;
You don't need to cast malloc, and you need one extra character for the terminating '\0'
char *ans = malloc(1 + newleng);
size_t pos = 0;
Since you already have the length, use it also the same sizeof error
for(size_t i=0 ; i < sentenceLength ; i++, pos++){
if (sentence[i] == ' ') {
ans[pos] = '%';
ans[pos + 1] = '2';
ans[pos + 2] = '0';
You are incrementing pos at every iteration so here you increment it by 2
pos += 2;
} else {
ans[pos] = sentence[i];
}
}
pos + 1 is wrong, you already increment it in the loop.
ans[pos] = '\0';
printf("%lu\n", sentenceLength);
printf("%lu\n", pos);
printf("%s",ans);
/* Free memory and exit. */
free (ans);
return 0;
The complete fixed code
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
/* Maximum sentence size + 1. */
#define MAX_SENTENCE_SZ 256
int amountOfSpaces(char* str) {
int cnt=0;
while(*str!='\0') {
if(*str == ' ') {
cnt++;
}
str++;
}
return cnt;
}
int main(){
char sentence[100];
size_t sentenceLength;
/* Get the sentence, with size limit. */
fgets(sentence, sizeof(sentence), stdin);
sentenceLength = strlen(sentence);
/* Remove trailing newline, if there. */
if ((sentenceLength > 0) && (sentence[sentenceLength - 1] == '\0'))
sentence[--sentenceLength] = '\0';
int cant = amountOfSpaces(sentence);
int newleng = sentenceLength + 2 * cant;
char *ans = malloc(1 + newleng);
size_t pos = 0;
for(size_t i=0 ; i < sentenceLength ; i++, pos++) {
if (sentence[i] == ' ') {
ans[pos] = '%';
ans[pos + 1] = '2';
ans[pos + 2] = '0';
pos += 2;
} else {
ans[pos] = sentence[i];
}
}
ans[pos] = '\0';
printf("%lu\n", (unsigned long)sentenceLength);
printf("%lu\n", (unsigned long)pos);
printf("%s",ans);
/* Free memory and exit. */
free (ans);
return 0;
}

Answer 2

...I'm not able to find [...] what's causing me this problem.
Start using a debugger, get familiar with it.
Anyway:
if (sentence[i] == ' ') {
ans[pos] = '%';
ans[pos + 1] = '2';
ans[pos + 2] = '0';
pos += 2; // <<<<< BUG HERE -- increment by 2 not 3
} else {
Because pos is already incremented by 1 at each for iteration.
Btw: instead of using sizeof(sentence) store the actual length of the string in a variable and use that:
int l = strlen(sentence);
Remember l won't include the trailing null character.