C Program to concatenate string without using strcat()

In this C Programming example, we will implement the program to concatenate string without using strcat() and print the output on the console.

1. What is String Concatenation?

String Concatenation is a process when one string is appended to the end of another string.

Example 1:
Input: The first string: Codingeek
       The second string: .com
Output: 
After the concatenation: Codingeek.com

Helpful topics to understand this program better are-

• Data Types in C
• Console Input / Output in C
• Functions in C
• For and While Loop in C

2. C Program to concatenate string without using strcat()

Let’s discuss the execution(kind of pseudocode) for the program to concatenate string without using strcat() in C.

1. Initially, the program will prompt the user to enter two strings for the concatenation.
2. Then we invoke the method concatenateString().
3. In void concatenateString(), while and for loops are used to iterate the length of the string and append the first string to the end of the other.
4. After the concatenation, the concatenated string is printed on the console.

Let us now implement the above execution of the program to concatenate two strings without using strcat() in C.

#include <stdio.h>
char s1[100], s2[100], j;
int length;
length = 0;
void concatenateString(){
  while (s1[length] != '\0') {
    ++length;
  }
  for (j = 0; s2[j] != '\0'; ++j, ++length) {
    s1[length] = s2[j];
  }
  s1[length] = '\0';
}
int main() {
  printf("\nEnter the first string: ");
  scanf("%s",s1);
  printf("\nEnter the second string: ");
  scanf("%s",s2);
  concatenateString();
  printf("After the concatenation: ");
  puts(s1);
  return 0;
}

Note: The characters entered must be within the range declared in char[] data type and no spaces must be entered within the characters.

Output
Enter the first string: coding
Enter the second string: eek
After the concatenation: codingeek

3. Conclusion

In this C Programming example, we have discussed what is String concatenation and how to concatenate string without using strcat() method.

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