C++ Program to Find Substring in String with Explanation
C++
Medium
Strings
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1 min read
177 words
This problem helps you practice core C++ fundamentals in a practical way. It builds intuition around found, search, substring. Let’s break it down step by step so you can implement it confidently.
Problem Statement
Check if one string exists inside another string.
Real Life: Search functionality in text.
Input Format
Two strings:
• str1 → main string
• str2 → string to search
Output Format
Print
• Found
OR
• Not Found
Constraints
• Strings length ≥ 1
• Case-sensitive
• Use basic string logic
Concept Explanation
We need to check whether str2 exists inside str1.
This is like a search feature in text editors or websites.
Step-by-Step Logic
1.Take input strings str1 and str2.
2.Get lengths of both strings.
3.Loop through str1 from index 0 to (len1 - len2).
4.For each position, compare characters of str2 with str1.
5.If all characters match at any position:
• Print Found.
6.If no match is found after full loop:
• Print Not Found.
Code Solution
This explanation is written for learning purposes and to help beginners understand the concept clearly.
void string_q9_find_substring() {
string mainStr = "Programming in C plus plus";
string subStr = "plus";
int found = -1;
for(int i = 0; i <= mainStr.length() - subStr.length(); i++) {
bool match = true;
for(int j = 0; j < subStr.length(); j++) {
if(mainStr[i + j] != subStr[j]) {
match = false;
break;
}
}
if(match) {
found = i;
break;
}
}
if(found != -1) {
cout << "Substring found at position: " << found << endl;
} else {
cout << "Substring not found" << endl;
}
}
Output Example
Input:
programming is fun
is
Common Mistakes
- Misreading input/output format.
- Not handling constraints and edge cases.
- Off-by-one errors in loops.
- Forgetting to reset variables between test cases (if any).
Solution Guide
Problem
Check if one string exists inside another string.
Real Life: Search functionality in text.
Input / Output
Input
Two strings:
• str1 → main string
• str2 → string to search
Output
Print
• Found
OR
• Not Found
Constraints
• Strings length ≥ 1
• Case-sensitive
• Use basic string logic
Examples
Input:
programming is fun
is
Explanation
Concept Explanation
We need to check whether str2 exists inside str1.
This is like a search feature in text editors or websites.
Step-by-Step Explanation
1.Take input strings str1 and str2.
2.Get lengths of both strings.
3.Loop through str1 from index 0 to (len1 - len2).
4.For each position, compare characters of str2 with str1.
5.If all characters match at any position:
• Print Found.
6.If no match is found after full loop:
• Print Not Found.
Details
Common Mistakes
- Misreading input/output format.
- Not handling constraints and edge cases.
- Off-by-one errors in loops.
- Forgetting to reset variables between test cases (if any).
Official Solution
void string_q9_find_substring() {
string mainStr = "Programming in C plus plus";
string subStr = "plus";
int found = -1;
for(int i = 0; i <= mainStr.length() - subStr.length(); i++) {
bool match = true;
for(int j = 0; j < subStr.length(); j++) {
if(mainStr[i + j] != subStr[j]) {
match = false;
break;
}
}
if(match) {
found = i;
break;
}
}
if(found != -1) {
cout << "Substring found at position: " << found << endl;
} else {
cout << "Substring not found" << endl;
}
}
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