c++ - ReplaceSubstring function glitch -

i'm working on function accepts 3 c-strings , objective replace word user finds anywhere on sentence 1 he/she inputs.

below code of function:

void replacesubstring(char str1[], char str2[], char str3[]) {     char *a= new char(sizeof(str1));     char *b= new char(sizeof(str1));      int len=0;     for(unsigned int ind= 0; ind< sizeof(str1); ind++)     {         for(unsigned ind1= 0; ind1< sizeof(str2); ind1++)             a[ind]= str1[ind+ ind1];             a[ind]= '\0';              if(strcmp(str1, str2))             {                 for(unsigned int y= 0; y< sizeof(str3); y++)                 {                     b[len]= str3[y];                     len++;                 }                     ind+= (sizeof(str2)- 1);             }             else             {                 cout<< "error! no match found!"<< endl;             }     }     cout<< b<< endl; } 

let show example of output:

1. enter string: i love mangoes

2. enter word want for: mangoes

3. enter new word replace "mangoes" with: cheese

4. output? chee─

can explain can improve , why causing glitch? info appreciated.

p.s: i've tried working strstr, strstr returns pointer , leaves sentence cut off , worried figuring out way skip characters end of sentence word , figuring out afterwards. how using strstr, if possible, without cutting sentence?

thank help.

you compare str1 , str2 stcmp instead of , str2 . strcmp returns 0 (= false) when strings equal. b completed chars str3, , not recopy str1.