String modification

Learn string modification with .replace() and .insert().

Replacing parts with replace

The .replace() method of the string class replaces a part of the string starting at a given position with another string. The first parameter is the start position, the second is the number of characters to remove, and the third is the replacement string.

string s = "hello world";
s.replace(6, 5, "c++");  // "hello c++"

Here, starting at position 6, 5 characters ("world") are removed and "c++" is put in their place. Positions are zero-based; s[0] is the first character. You can learn the string length with the .size() method.

Inserting with insert

The .insert() method inserts a string at a given position; existing characters shift to the right. The first parameter is the position, the second is the string to insert.

string s = "hello";
s.insert(0, "hi ");  // "hi hello"

Here "hi " is inserted at position 0; the original "hello" shifts right. With insert you can place new pieces at the start, middle, or end of a string; the string grows automatically.

Exercise Replace a part with replace

Define string s = "hello world";. Use s.replace(6, 5, "c++"); to remove 5 characters at position 6 and put "c++" in their place. Then print it with cout << s << endl;.

Show example solution

#include <iostream>
#include <string>
using namespace std;

int main() {
    string s = "hello world";
    s.replace(6, 5, "c++");
    cout << s << endl;
    return 0;
}

Test yourself

Fill in the blank: replace call

string s = "green leaf";
s.____(6, 5, "bird");

Show answer

string s = "green leaf";
s.replace(6, 5, "bird");

What does s.insert(0, "x") do?
- Inserts "x" at the start of s
- Appends "x" to the end of s
- Removes the first character of s
- Replaces s with "x"
Show answer

Inserts "x" at the start of s — Position 0 means the start; "x" is added at the beginning.
Match each method with its job

replace

Swaps a part
insert

Inserts in the middle
size

Returns length

Next lesson: Summary - Advanced strings

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